The research presented in this thesis includes a detailed investigation into factors influencing ionic conductivity in the crystalline polymer electrolyte PEO₆:LiPF₆. It has previously been shown that preparing PEO₆:LiPF₆ with PEO modified with larger –OC₂H₅ end groups increases ionic conductivity by one order of magnitude [¹],primarily due to disruption of the crystal structure caused by the inclusion of the larger end groups. In this study it is shown that by reducing PEO molecular weight in crystalline PEO₆:LiPF₆ ionic conductivity is also increased. This was attributed to an increasing concentration of polymer chain end regions upon lowering molecular weight resulting in the creation of more defects, as well as possible increases in crystallite size resulting in longer continuous pathways for ion transport. Similar results were observed using both polydispersed and monodispersed PEO to prepare complexes. In addition, it is demonstrated here that ionic conductivity in crystalline polymerelectrolytes is not confined to PEO₆:LiXF₆ (X=P, As, Sb)[²][³] type materials. The structures and ionic conductivity data are reported for a series of new crystalline polymer complexes: the alkali metal electrolytes. They are composed of low molecular weight PEO and different alkali metal hexafluoro salts (Na⁺, K⁺ and Rb⁺), and include the best conductor poly(ethylene oxide)₈:NaAsF₆ discovered to date [⁴], with a conductivity 1.5 orders of magnitude higher than poly(ethylene oxide)₆:LiAsF₆. A new class of solid ion conductor is reported: the crystalline small-molecule electrolytes. Such materials consist of lithium salts dissolved in low molecular weight glyme molecules [CH₃O(CH₂CH₂O)[subscript(n)]CH₃, n=1-12], forming crystalline complexes [⁵][⁶]. These materials are soft solids unlike ceramic electrolytes and unlike polymer electrolytes they are highly crystalline, are of low molecular weight and have no polydispersity. By varying the number of repeat units in the glyme molecule, many complexes may be prepared with a wide variety of structures. Here, ionic conductivity and cation transference number (t₊) data for several such complexes is presented [⁷][⁸][⁹].These complexes have appreciable ionic conductivities for crystalline complexes and their t₊ values vary markedly depending on the glyme molecule utilized. The differences in t₊ values can be directly attributed to differences in their crystal structures. [¹] Staunton, E., Andreev, Y.G. & Bruce, P.G. Factors influencing the conductivity of crystalline polymer electrolytes. Faraday Discussions 134, 143-156 (2007). [²] Gadjourova, Z., Andreev, Y.G., Tunstall, D.P. & Bruce, P.G. Ionic conductivity in crystalline polymer electrolytes. Nature 412, 6846 (2001). [³] Stoeva, Z., Martin-Litas, I., Staunton, I., Andreev, Y.G. & Bruce, B.G. Ionic Conductivity in the Crystalline Polymer Electrolytes PEO₆:LiXF₆, X = P, As, Sb. J. Am. Chem. Soc. 125, 4619-4626(2003). [⁴] Zhang, C., Gamble, S., Ainsworth, D., Slawin, A.M.Z., Andreev, Y.G. & Bruce, P.G. Alkali metal crystalline polymer electrolytes. Nature Materials 8, 580-584 (2009). [⁵] Henderson, W.A., Brooks, N.R., Brennessel, W.W. & Young Jr, V.G. Triglyme-Li⁺ Cation Solvate Structures: Models for Amorphous Concentrated Liquid and Polymer Electrolytes (I). Chem. Mater. 15, 4679-4684 (2003). [⁶] Henderson, W.A., Brooks, N.R. & Young Jr, V.G. Tetraglyme-Li⁺ Cation Solvate Structures: Models for Amorphous Concentrated Liquid and Polymer Electrolytes (II). Chem. Mater. 15, 4685-4690 (2003). [⁷] Zhang, C., Andreev, Y.G. & Bruce, P.G. Crystalline small-molecule electrolytes. Angewandte Chemie, International Edition 46, 2848-2850 (2007). [⁸] Zhang, C., Ainsworth, D., Andreev, Y.G. & Bruce, P.G. Ionic Conductivity in the Solid Glyme Complexes [CH₃O(CH₂CH₂O)[subscript(n)]CH₃]:LiAsF₆ (n = 3,4). J. Am. Chem. Soc. 129, 8700- 8701 (2007). [⁹] Zhang, C., Lilley, S.J., Ainsworth, D., Staunton, E., Andreev, Y.G., Slawin, A.M.Z. & Bruce, P.G. Structure and Conductivity of Small-Molecule Electrolytes [CH₃O(CH₂CH₂O)[subscript(n)]CH₃]:LiAsF₆ (n = 8-12). Chem. Mater. 20, 4039-4044 (2008).

Lithium-ion batteries with higher capacity and longer cycle life than that available today are required as secondary energy sources for a wide range of emerging applications. In particular, the cycling performance of several candidate materials for lithium-ion battery electrodes is insufficient because of the fast capacity fading and short cycle life, which is mainly a result of mechanical degradation. This dissertation mainly focuses on the issue of mechanical degradation in advanced lithium-ion battery electrodes. Thin films of tin electrodes were studied where we observed whisker growth as a result of electrochemical cycling. These whiskers bring safety concerns because they may penetrate through the separator, and cause short-circuit of the electrochemical cells. Cracking patterns generated in amorphous silicon thin film electrodes because of electrochemical cycling were observed and analyzed. A two-dimensional spring-block model was proposed to successfully simulate the observed cracking patterns. With semi-quantitative study of the cracking pattern features, two strategies to void cracking in thin-film electrodes were proposed, namely reducing the film thickness and patterning the thin-film electrodes. We also investigated electrodes consisting of low melting point elements and showed that cracks can be self-healed by the solid-to-liquid phase transformation upon cycling. Using gallium as an example, mechanical degradation as a failure mechanism for lithium-ion battery electrodes can be eliminated. In order to quantitatively understand the effect of surface modification on electrodes, we analyzed diffusion equations with boundary conditions of finite interfacial reactions, and proposed a modified potentialstatic intermittent titration technique (PITT) as an electro-analytical technique to study diffusion and interfacial kinetics. The modified PITT has been extended to thin-film geometry and spherical geometry, and thus can be used to study thin-film and composite electrodes consisting of particles as active materials.

The focus of this dissertation is to utilize chemical functionalization as a probe to investigate the reactivity of N-doped multiwalled carbon nanotubes (N-MWCNTs). The surface of N-MWCNTs, being a set of potentially reactive graphene edges, provides a large number of reactive sites for chemical modification, so considerable changes in chemical and physical properties can be envisaged. We observed that both reduction (dissolving metal reduction/alkylation) and oxidation (H2SO4/HNO3 and H2SO4/KMnO4 mixtures) of N-MWCNTs lead to formation of interesting spiral channels and spiraled carbon nanoribbons. A variety of techniques, including TGA, SEM, TEM, XRD and surface area measurements were used to analyze these new textural changes. We have developed methods to demonstrate that specific chemistry has occurred on these new structures. To this end, we introduced metal-binding ligands that could be used as probes in imaging and spectroscopic techniques including TEM, STEM, EDX, and EELS. A proposal for the underlying structure of N-MWCNTs responsible for the formation of the new textures is presented. We have investigated the performance of our materials as potential negative electrodes for rechargeable lithium ion batteries.

Carbon nano-onions (CNOs) discovered by Ugarte in 1992 are multi-layered fullerenes that are spherical analogs of multi-walled carbon nanotubes with diameters varying from 6 nm to 30 nm. Among the various methods of synthesis, CNOs prepared by graphitization of nanodiamonds (N-CNOs) and underwater electric arc of graphite rods (A-CNOs) are the subject of our research. N-CNOs are considered as more reactive than A-CNOs due to their smaller size, high curvature and surface defects. This dissertation focuses on structural analysis and surface functionalization of N- CNOs with diameters ranging from 6—10 nm. Synthetic approaches such as oleum- assisted oxidation, Freidel-Crafts acylation and Billups reductive alkylation were used to functionalize N-CNOs to improve their dispersion properties in aqueous and organic solvents. Functionalized N-CNOs were characterized using various techniques such as TGA, TG-MS, Raman spectroscopy and pH-titrimetry. We designed an experimental method to isolate polycyclic aromatic adsorbates formed on the surface of oleum oxidized N-CNOs (ON-CNOs) and characterized them. A-CNOs, on the other hand are bigger than N-CNOs with diameters ranging from 20—40 nm. In this dissertation, we discuss the preparation of graphene structures by unzipping of A-CNOs using KMnO4 as oxidizing agent. These graphene structures were characterized using powder X-ray diffraction, TGA, BET nitrogen adsorption/desorption studies and compressed powder conductivity. This dissertation also focuses on lithiation/delithiation studies of N-CNOs, A- CNOs and A-CNO-derived graphene structures to use them as negative electrode materials in lithium-ion batteries. The cycling performances of these materials at a charge/discharge rate of C/10 were discussed. The cycling performance of N-CNOs was tested at faster charge/discharge rate of C.

Currently, automotive batteries use intercalation cathodes such as lithium iron phosphate (LiFePO4) which provide high levels of safety while sacrificing cell voltage and therefore energy density. Lithium transition metal oxide (LiMO2) batteries achieve higher cell voltages at the risk of releasing oxygen gas during charging, which can lead to ignition of the liquid electrolyte. To achieve both safety and high energy density, oxide cathodes must be well characterized under operating conditions. In any intercalation cathode material, the loss of positive lithium ions during charge must be balanced by the loss of negative electrons from the host material. Ideally, the TM ions oxidize to compensate this charge. Alarmingly, the stoichiometry of the latest LiMO2 cathode materials includes more lithium ions than the TM ions can compensate for. Inevitably, peroxide ions or dioxygen gas must form. The former mechanism is vital for lithium-air batteries, while the latter must be avoided. Battery researchers have long sought to completely characterize the intercalation reaction in working batteries. However, the volatile electrolytes employed in batteries are not compatible with vacuum-based characterization techniques, nor are the packaging materials required to contain the liquid. For the first time, a solid state battery (using exposed particles of Li1.17Ni0.25Mn0.58O2) was charged while using soft X-ray absorption spectroscopy to observe the redox trends in nickel, manganese and oxygen. This was combined with innovative hard X-ray absorption spectroscopic studies on the same material to create the most complete picture yet possible of charge compensation.

Lithium-ion battery (LIB) technology is currently the most promising candidate for power sources in applications such as portable electronics and electric vehicles. In today's state-of-the-art LIBs, non-aqueous electrolytes are the most widely used family of electrolytes. In the present thesis work, efforts are devoted to improve the conventional LiPF6-based electrolytes with additives, as well as to develop alternative lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI)-based electrolytes for silicon anodes. In addition, electrode/electrolyte interfacial chemistries in such battery systems are extensively investigated. Two additives, LiTDI and fluoroethylene carbonate (FEC), are evaluated individually for conventional LiPF6-based electrolytes combined with various electrode materials. Introduction of each of the two additives leads to improved battery performance, although the underlying mechanisms are rather different. The LiTDI additive is able to scavenge moisture in the electrolyte, and as a result, enhance the chemical stability of LiPF6-based electrolytes even at extreme conditions such as storage under high moisture content and at elevated temperatures. In addition, it is demonstrated that LiTDI significantly influences the electrode/electrolyte interfaces in NMC/Li and NMC/graphite cells. On the other hand, FEC promotes electrode/electrolyte interfacial stability via formation of a stable solid electrolyte interphase (SEI) layer, which consists of FEC-derivatives such as LiF and polycarbonates in particular. Moreover, LiTDI-based electrolytes are developed as an alternative to LiPF6 electrolytes for silicon anodes. Due to severe salt and solvent degradation, silicon anodes with the LiTDI-baseline electrolyte showed rather poor electrochemical performance. However, with the SEI-forming additives of FEC and VC, the cycling performance of such battery system is greatly improved, owing to a stabilized electrode/electrolyte interface. This thesis work highlights that cooperation of appropriate electrolyte additives is an effective yet simple approach to enhance battery performance, and in addition, that the interfacial chemistries are of particular importance to deeply understand battery behavior.

Background:          The growing number of electric vehicles gives rise to a whole new reverse supply chain. Once the electric vehicle batteries reach their end-of-life, societal and governmental pressure forces automotive manufacturers to set up a network for disposing the hazardous batteries. Although, the volumes of returned batteries remain low, volumes will increase in upcoming years. Current networks and processes related to the return flow of electric vehicle batteries are not well established, nor well defined. Thus, creating an urgency to develop efficient collection networks.   Purpose:                  The purpose of this study is to investigate how reverse logistics networks are currently set up and to provide an overview of how the different actors and processes are connected. In addition, this thesis aims to identify challenges encountered by logistics providers and recyclers. By doing so, we hope to contribute to the research gap of which factors that constitutes a bottleneck for further development of the reverse logistics chain of electric vehicle batteries.   Method:                  The thesis conducts an interview study and is qualitative in nature. Semi-structured interviews generated empirical data, which was analysed through cross-case analysis incorporating a thematic analysis. Through this analysis we were able to achieve new theoretical understandings in connection to institutional theory.   Conclusion:             Through empirical findings a detailed framework of the reverse logistics chain of EVBs is portrayed. Furthermore, different challenges span over the processes illustrated in the framework. This presents an overview which is not found in current literature and extends current research on this topic.

Thesis advisor: Udayan Mohanty / Rechargeable batteries, especially lithium ion batteries, have greatly transformed mobile electronic devices nowadays. Due to the ever-depletion of fossil fuel and the need to reduce CO2 emissions, the development of batteries needs to extend the success in small electronic devices to other fields such as electric vehicles and large-scale renewable energy storage. Li-ion batteries, however, even when fully developed, may not meet the requirements for future electric vehicles and grid-scale energy storage due to the inherent limitations related with intercalation chemistry. As such, alternative battery systems should be developed in order to meet these important future applications. This dissertation presents our successes in improving Li-O2 battery performance for electric vehicle application and integrating a redox flow battery into a photoelectrochemical cell for direct solar energy storage application. Li-O2 batteries have attracted much attention in recent years for electric vehicle application since it offers much higher gravimetric energy density than Li-ion ones. However, the development of this technology has been greatly hindered by the poor cycling performance. The key reason is the instability of carbon cathode under operation conditions. Our strategy is to protect the carbon cathode from reactive intermediates by a thin uniform layer grown by atomic layer depostion. The protected electrode significantly minimized parasitic reactions and enhanced cycling performance. Furthermore, the well-defined pore structures in our carbon electrode also enabled the fundamental studies of cathode reactions. Redox flow batteries (RFB), on the other hand, are well-suited for large-scale stationary energy storage in general, and for intermittent, renewable energy storage in particular. The efficient capture, storage and dispatch of renewable solar energy are major challenges to expand solar energy utilization. Solar rechargeable redox flow batteries (SRFBs) offer a highly promising solution by directly converting and storing solar energy in a RFB with the integration of a photoelectrochemical cell. One major challenge in this field is the low cell open-circuit potential, mainly due to the insufficient photovoltages of the photoelectrode systems. By combining two highly efficient photoelectrodes, Ta3N5 and Si (coated with GaN), we show that a high-voltage SRFB could be unassistedly photocharged and discharged with a high solar-to-chemical efficiency. / Thesis (PhD) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Un modèle décrivant les phénomènes physiques internes de batteries lithium-ion est développé pour une détection précise de leur état, avec application au domaine de l'industrie automobile. Pour pouvoir utiliser le modèle à des fins de contrôle de charge rapide, un observateur de vieillissement est tout d'abord conçu et intégré au modèle de batterie. Dans un second temps, une stratégie de contrôle de charge rapide robuste est conçue. Elle est basée sur un contrôleur Crone capable de gérer les grandes incertitudes paramétriques du modèle de batterie tout en atteignant l'objectif de charge rapide. Enfin, quelques simplifications du modèle de batterie, de la technique d'optimisation et de la définition des profils de charge rapide sont proposées et évaluées afin de rendre l'ensemble de la stratégie de recharge rapide applicable à un système embarqué de gestion de batterie. / A physics-based battery model is developed for an accurate state-detection of batteries in the automotive industry. In order to use the model for the purpose of fast charging control an aging observer is designed and integrated to the battery model. In a subsequent step a robust fast charging control is introduced to design a controller able to deal with large parametric uncertainties of the battery model while achieving the fast charging target. Finally some simplifications in the battery model structure, in the optimization technique and in the definition of fast charging profiles are proposed and evaluated to make the whole model applicable for an onboard battery management system.

The rechargeable secondary Lithium ion (Li-ion) battery is expected to grow to more than $6.3 billion by 2012 from ~$4.6 billion in 2006. With the development of personnel electronics, hybrid and electric vehicles, Li-ion batteries will be more in demand. However, Li-ion batteries are not widely recycled because it is not economically justifiable (in contrast, at present more than 97% Lead-acid batteries are recycled). So far, no commercial methods are available to recycle different chemical Li-ion batteries economically and efficiently. Considering our limited resources, environmental impact, and national security, Li-ion batteries must be recycled. A new methodology with low temperature and high efficiency is proposed in order to recycle Li-ion batteries economically and with industrial viability. The separation and synthesis of cathode materials (most valuable in Li-ion batteries) from recycled components are the main focus of the proposed research. The analytical results showed that the recycling process is practical and has high recovery efficiency, create great commercial value as well.