Doctor of Philosophy / Department of Chemistry / Jun Li / Electrical energy storage (EES) is crucial in todays’ society owing to the advances in electric cars, microelectronics, portable electronics and grid storage backup for renewable energy utilization. Lithium ion batteries (LIBs) have dominated the EES market owing to their wide use in portable electronics. Despite the success, low specific capacity and low power rates still need to be addressed to meet the increasing demands. Particularly, the low specific capacity of cathode materials is currently limiting the energy storage capability of LIBs. Vanadium pentoxide (V₂O₅) has been an emerging cathode material owing to its low cost, high electrode potential in lithium-extracted state (up to 4.0 V), and high specific capacities of 294 mAh g⁻¹ (for a 2 Li⁺/V₂O₅ insertion process) and 441 mAh g⁻¹ (for a 3 Li⁺/V₂O₅ insertion process). However, the low electrical conductivities and slow Li⁺ ion diffusion still limit the power rate of V₂O₅. To enhance the power-rate capability we construct two core-shell structures that can achieve stable 2 and 3 Li⁺ insertion at high rates. In the first approach, uniform coaxial V₂O₅ shells are coated onto electrospun carbon nanofiber (CNF) cores via pulsed electrodeposition. The materials analyses confirm that the V₂O₅ shell after 4 hours of thermal annealing at 300 °C is a partially hydrated amorphous structure. SEM and TEM images indicate that the uniform 30 to 50 nm thick V₂O₅ shell forms an intimate interface with the CNF core. Lithium insertion capacities up to 291 and 429 mAh g⁻¹ are achieved in the voltage ranges of 4.0 – 2.0 V and 4.0 – 1.5 V, respectively, which are in good agreement with the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion. Moreover, after 100 cycles, remarkable retention rates of 97% and 70% are obtained for 2 and 3 Li⁺/V₂O₅ insertion, respectively. In the second approach, we implement a three-dimensional (3D) core-shell structure consisting of coaxial V₂O₅ shells sputter-coated on vertically aligned carbon nanofiber (VACNF) cores. The hydrated amorphous microporous structure in the “as-deposited” V₂O₅ shells and the particulated nano-crystalline V₂O₅ structure formed by thermal annealing are compared. The former provides remarkably high capacity of 360 and 547 mAh g⁻¹ in the voltage range of 4.0 – 2.0 V and 4.0 – 1.5 V, respectively, far exceeding the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion, respectively. After 100 cycles of 3 Li⁺/V₂O₅ insertion/extraction at 0.20 A g⁻¹ (~ C/3), ~ 84% of the initial capacity is retained. After thermal annealing, the core-shell structure presents a capacity of 294 and 390 mAh g⁻¹, matching well with the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion. The annealed sample shows further improved stability, with remarkable capacity retention of ~100% and ~88% for 2 and 3 Li⁺/V₂O₅ insertion/extraction. However, due to the high cost of Li. alternative approaches are currently being pursued for large scale production. Sodium ion batteries (SIB) have been at the forefront of this endeavor. Here we investigate the sodium insertion in the hydrate amorphous V₂O₅ using the VACNF core-shell structure. Electrochemical characterization was carried out in the potential ranges of 3.5 – 1.0, 4.0 – 1.5, and 4.0 – 1.0 (vs Na/Na⁺). An insertion capacity of 196 mAh g-1 is achieved in the potential range of 3.5 – 1.0 V (vs Na/Na⁺) at a rate of 250 mA g⁻¹. When the potential window is shifted upwards to 4.0 – 1.5 V (vs Na/Na⁺) an insertion capacity of 145 mAh g⁻¹ is achieved. Moreover, a coulombic efficiency of ~98% is attained at a rate of 1500 mA g⁻¹. To enhance the energy density of the VACNF-V₂O₅ core-shell structures, the potential window is expanded to 4.0 – 1.0 V (vs Na/Na⁺) which achieved an initial insertion capacity of 277 mAh g⁻¹. The results demonstrate that amorphous V₂O₅ could serve as a cathode material in future SIBs.

<p>The single particle model was extended to include electrode and particle volume expansion effects observed in high capacity alloying electrodes. The model was used to predict voltage profiles in sodium ion batteries with tin and tin-phosphide negative electrodes. It was seen that the profiles predicted by the modified model were significantly better than the classical model. A parametric study was done to understand the impact of properties such as particle radius, diffusivity, reaction rate etc on the performance of the electrode. The model was also modified for incorporating particles having a cylindrical morphology. For the same material properties, it was seen that cylindrical particles outperform spherical particles for large L/R values in the cylinder due to the diffusion limitations at low L/R ratios. A lattice spring-based degradation model was used to observe crack formation and creep relaxation within the particle. It was observed that the fraction of broken bonds increases with an increase in strain rate. At low strain rates, it was seen that there was a significant expansion in particle volumes due to creep deformation. This expansion helped release particle stresses subsequently reducing the amount of fracture.</p>

Conversion material electrodes such as FeF2 possess the potential to deliver transformative improvements in lithium ion battery performance because they permit a reversible change of more than one Li-ion per 3d metal cation. They outperform current state of the art intercalation cathodes such as LiCoO2, which have volumetric and gravimetric energy densities that are intrinsically limited by single electron transfer. Current studies focus on composite electrodes that are formed by mixing with carbon (FeF2-C), wherein the carbon is expected to act as a binder to support the matrix and facilitate electronic conduction. These binders complicate the understanding of the electrode-electrolyte interface (SEI) passivation layer growth, of Li agglomeration, of ion and electron transport, and of the basic phase transformation processes under electrochemical cycling. This research uses thin-films as a model platform for obtaining basic understanding to the structural and chemical foundations of the phase conversion processes. Thin film cathodes are free of the binders used in nanocomposite structures and may potentially provide direct basic insight to the evolution of the SEI passivation layer, electron and ion transport, and the electrochemical behavior of true complex phases. The present work consisted of three main tasks (1) Development of optimized processes to deposit FeF2 and LiPON thin-films with the required phase purity and microstructure; (2) Understanding their electron and ion transport properties and; (3) Obtaining insight to the correlation between structure and capacity in thin-film microbatteries with FeF2 thin-film cathode and LiPON thin-film solid electrolyte. Optimized pulsed laser deposition (PLD) growth produced polycrystalline FeF2 films with excellent phase purity and P42/mnm crystallographic symmetry. A schematic band diagram was deduced using a combination of UPS, XPS and UV-Vis spectroscopies. Room temperature Hall measurements reveal that as-deposited FeF2 is n-type with an electron mobility of 0.33 cm2/V.s and a resistivity was 0.255 Ω.cm. The LiPON films were deposited by reactive sputtering in nitrogen, and the results indicate that the ionic conductivity is dependent on the amount of nitrogen incorporated into the film during processing. The highest ionic conductivity obtained was 1.431.9E-6 Scm-1 and corresponded to a chemical composition of Li1.9PO3.3N.21. FeF2/LiPON thin films microbatteries were assembled using a 2032 coin cell configuration and subjected to Galvanostatic cycling. HRTEM and EELS spectroscopy where performed across the FeF2/LiPON interface of samples cycled once 15 times in their lithiated and delithiated states to understand the relationship between microstructural evolution and capacity. The EELS measurements provided evidence of a three-phase conversion reaction over the first discharge described by FeF2 +2e-+2Li+↔Fe +LiF, and of incomplete reconversion back to FeF2 after the 1st cycle resulting in new Fe0 and LiF phases in delithiated samples. This incomplete conversion results in (a) a smaller phase fraction of FeF2 participating in the conversion process subsequently and (b) the formation of LiF which is resistive to both electron and ion transport. This results in the observed drastic drop in capacity after the1st cycle. More study to understand the reconversion reaction pathways is required to fully exploit the potential of FeF2 and other conversion materials as cathodes in Li ion batteries.

In today’s fast adjustment to renewable energy, new battery technologies are needed to meetthe ever-growing demands of energy storage. Cheaper and easier to produce materials areneeded, as well as materials with a lower environmental impact. One new and interestingtechnology is the dual-ion battery, and more specifically the aluminum dual-ion battery. Thisbattery uses cheap and abundant aluminum together with a graphitic cathode to work. However,a lot of research today uses expensive and sophisticated cathode materials to make this type ofbattery work. Therefore, this thesis focuses on creating a cheap and easy to produce graphitecathode material through the phase inversion method for the use in aluminum dual-ionbatteries, that is also freestanding for better energy density. Graphene is also used as anadditive to improve the electrical conductivity of the material, and the material is later tested in afull cell with the typical ionc liquid electrolyte EMImCL/AlCl4.Through phase inversion, a freestanding graphite cathode is produced with 8 wt% PVDF binderand 0.4 wt% graphene. The material has a porous structure and an enhanced electricalconductivity with the graphene added. Through CV cycling and symmetric Al-Al tests the batteryreactions are shown to work. However, when cycling the cell with a constant current there areproblems, probably coming from some sort of soft shorting or side reactions. It is revealed thatapart from the expected reactions, Ni dissolution from the contact tabs also takes place, andmay cause problems. Further tests are needed to validate if this material works. However,because no new active materials have been introduced to the battery chemistry, it is reasonableto believe that the battery will work with some small changes.Tek nisk-naturvetensk apliga fak ulteten, Upps ala universitet. Utgiv nings ort U pps al a/Vis by . H andledare: Anwar Ahniy az , Äm nesgranskar e: D aniel Brandell, Ex aminator: Lena Klintberg

This thesis concerns the use of advanced solid-state NMR methods to investigate local structural features and ion dynamics in a series of paramagnetic cathode materials for lithium and sodium ion batteries. A variety of polyanionic phosphate and fluorophosphate derivatives were explored to identify characteristics that ultimately improve battery performance. Solid-state NMR is an excellent method to probe such materials, as it offers the unique ability to track the charge-carrying alkali ion (Li or Na) over the course of the electrochemical process, adding insight not obtainable by bulk characterization techniques. Selective inversion exchange experiments were used to elucidate ion diffusion pathways in low-mobility Li ion conductors Li2MnP2O7 and Li2SnO3. Contrasting experimental results highlight significant differences observed when the method is applied to paramagnetic versus diamagnetic systems, with the former being much more complicated to study with traditional exchange spectroscopy methods. Selective inversion was similarly applied to a new lithium iron vanadate framework, LiFeV2O7, where the changing ion dynamics as a function of electrochemical state of charge were quantified, allowing for the development of a model to explain the corresponding phase changes in the material. This represents the first example of an ex situ Li-Li exchange study for a cathode material, particularly where the conductivity changes are linked directly to a change of ion exchange rates. Additionally, 23Na NMR spectroscopy was additionally used to investigate Na2FePO4F as a potential Na ion battery cathode, where ex situ NMR measurements successfully determined the local Na ion distribution in the electrode as a function of electrochemical cycling. In combination with density functional theory (DFT) calculations, the NMR results lead to the construction of a biphasic desodiation model for Na2FePO4F cathodes. Finally, possible defect formation in sodium iron fluorophosphate was investigated with a variety of methods including 23Na NMR, DFT calculations, powder X-ray diffraction and Mössbauer spectroscopy. / Thesis / Doctor of Philosophy (PhD) / Lithium ion batteries are considered to be at the forefront of current energy storage development, offering high energy density in a small and lightweight package. This thesis delineates the investigation of materials for both lithium and sodium ion batteries via nuclear magnetic resonance methods. Slow Li ion dynamics were investigated and quantified in three lithium-conducting materials: Li2MnP2O7, Li2SnO3, and LiFeV2O7 via the use of selective inversion NMR experiments. In the case of the latter, the ion dynamics were probed ex situ during the course of battery cycling, where a maximum in Li mobility is observed approximately half way through the charge-discharge cycle. Additionally, a potential Na ion cathode material, Na2FePO4F, was found by ex situ methods to reveal a biphasic mechanism for the desodiation of the electrode during charging. This mechanism and the NMR data used to discover it were further supported by ab initio calculations.

Liu, Hao = 鋰離子電池納米電極的製備和表徵 / 劉昊. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 99-103). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Liu, Hao = Li li zi dian chi na mi dian ji de zhi bei he biao zheng / Liu Hao.

The main aim of this thesis is to reveal the chemical structures of the solid-liquid interphase in lithium ion batteries by NMR spectroscopy in order to understand the working mechanism of electrolyte additives for achieving stable cycling performance. In the first part, a combination of solution and solid-state NMR techniques, including dynamic nuclear polarization (DNP) are employed to monitor the formation of the solid electrolyte interphase (SEI) on next-generation, high-capacity Si anodes in conventional carbonate electrolytes with and without fluoroethylene carbonate (FEC) additives. A model system of silicon nanowire (SiNW) electrode is used to avoid interference from the polymeric binder. To facilitate characterization via one- and two-dimensional NMR, ^13C-enriched FEC was synthesized and used, ultimately allowing a detailed structural assignment of the organic SEI. FEC is found to first defluorinated to form soluble vinylene carbonate (VC) and vinoxyl species, which react to form both soluble and insoluble branched ethylene-oxide-based polymers. In the second part, the same methodology is applied to study the decomposition products of pure FEC or VC electrolytes containing 1 M LiPF_6. The pure FEC/VC system simplifies the electrolyte solvent formulation and avoids the interaction between different solvent molecules. Polymeric SEIs formed in pure FEC or VC electrolytes consist mainly of cross-linked PEO and aliphatic chain functionalities along with additional carbonate and carboxylate species. The presence of cross-linked PEO-type polymers in FEC and VC correlates with good capacity retention and high Coulombic efficiencies of the SiNWs anode. Using ^29Si DNP NMR, the interfacial region between SEI and the Si surface was probed for the first time with NMR spectroscopy. Organosiloxanes form upon cycling, confirming that some of the organic SEI is covalently bonded to the Si surface. It is suggested that both the polymeric structure of the SEI and the nature of its adhesion to the redox-active materials are important for electrochemical performance. Finally, the soluble decomposition products of EC formed during electrochemical cycling have been thoroughly analyzed by solution NMR and mass spectrometry, in order to explain the capacity-fading of Si anodes in a conventional EC-based electrolyte and address questions that arose when studying the additive-containing electrolytes. The detailed structures for the EC-degradation products are determined: a linear oligomer consist of ethylene oxide and carbonate units is observed as the major degradation product of EC.

Silicon has the highest theoretical capacity of any known anode material, and silicon coated carbon nanotubes (Si-CNTs) have shown promise of dramatically increasing battery capacity. However, capacity fading with cycling and low rate capability prevent widespread use. Here, three studies on differing aspects of these batteries are presented. Here, three studies on differing aspects of these batteries are presented. The first examines the rate capability of these batteries. It compares the cycling of electrodes hundreds of microns thick with and without ten micron access holes to facilitate diffusion. The holes do not improve rate capability, but thinner coatings of silicon do improve rate capability, indicating that the limiting mechanism is the diffusion through the nanoscale bulk silicon. The second attempts to enable stable cycling of anodes heavily loaded with silicon, using a novel monolithic scaffolding formed by coating vertically aligned carbon nanotubes (VACNTs) with nanocrystalline carbon. The structure was only able to stabilize the cycling at loadings of carbon greater than 60% of the electrode by volume. These electrodes have volume capacities of ~1000 mAhr/ml and retained over 725 mAhr/ml by cycle 100. The third studies the use of an encapsulation method to stabilize the solid electrolyte interphase (SEI) and exclude the electrolyte. The method was only able to stabilize cycling at loadings below 5% silicon, but exhibits specific capacities as high as 3000 mAhr/g of silicon after 20 cycles.

<p>The lucrative characteristics of high energy and power density from lithium-ion batteries have also become drawbacks when they are not handled appropriately. The reactive and flammable materials present within the cell raise safety concerns which need to be addressed. Aging of the cell components occurs in a natural way due to continuous cycling. Constant intercalation/deintercalation of Li-ions into the active materials induces stresses that in the long-term cycling mechanically modify the electrodes in an irreversible way. Also, electrode/electrolyte side reactions diminish the Li-ion inventory reducing the cell capacity and lifetime. Along with cell aging, intentional/unintentional abuse tests can occur at the hands of the final user. Improper handling and operation may lead the Li-ion cell to failure and possibly going into thermal runaway. This condition represents a threat to safety not only for cell integrity but also for user safety. Failure event can occur not only in brand new cells but also in aged cells. Current degradation studies focus either on the long-term aging degradation mechanisms or on fresh new cells’ abuse test. And few of them focused on the combination of both of them. </p>In this work, the degradation of Li-ion cells is investigated at different levels. First, at the electrode level, the effect of electrode processing and the intercalation properties of an anode and cathode materials is investigated. Then, at the cell level, abuse conditions such as external short, overcharge and overdischarge are studied in fresh and aged cells with different levels of degradation. Last but not least, the cells are assembled in a module configuration to investigate how a minor difference from one cell to another can affect the long-term performance. The aim is accomplished via a controlled lab test approach in order to get insights about the electrochemical, thermal and morphological changes that take place when the cell degrades.<br>

Batteries have found wide use in many household and industrial applications and since the 1990s, they have continued to rapidly shape the economy and social landscape of humans. Lithium ion batteries, a type of rechargeable batteries, have experienced a leap-frog development at technology and market share due to their prominent performance and environmental advantages and therefore, different forecasts have been made on the future trend for the lithium ion batteries in-terms of their use. The steady growth of energy demand for consumer electronics (CE) and electric vehicles (EV) have resulted in the increase of battery consumption and the electric vehicle (EV) market is the most promising market as it will consume a large amount of the lithium ion batteries and research in this area has reached advanced stages. This will consequently be resulting in an increase of metal-containing hazardous waste. Thus, to help prevent environmental and raw materials consumption, the recycling and recovery of the major valuable components of the spent lithium ion batteries appears to be beneficial. In this thesis, it was attempted to recover lithium from a synthetic slag produced using pyrometallurgy processing and later treated using hydrometallurgy. The entire work was done in the laboratory to mimic a base metal smelting slag. The samples used were smelted in a Tamman furnace under inert atmosphere until 1250oC was reached and then maintained at this temperature for two hours. The furnace was then switched off to cool for four hours and the temperature gradient during cooling was from 1250oC to 50oC. Lime was added as one of the sample materials to change the properties of the slag and eventually ease the possibility of selectively leaching lithium from the slag. It was observed after smelting that the slag samples had a colour ranging from dark grey to whitish grey among the samples.The X - ray diffractions done on the slag samples revealed that the main phases identified included fayalite (Fe2SiO4), magnetite (Fe3O4), ferrobustamine (CaFeO6Si2), Kilchoanite (Ca3Si2O7), iron oxide (Fe0.974O) and quartz (SiO2). The addition of lime created new compound in the slag with the calcium replacing the iron. The new phases formed included hedenbergite (Ca0.5Fe1.5Si2O6), ferrobustamine (CaFeO6Si2), Kilchoanite (Ca3Si2O7) while the addition of lithium carbonate created lithium iron (II) silicate (FeLi2O4Si) and dilithium iron silicate (FeLi2O4Si) phases.The Scanning Electron Microscopy (SEM) micrographs of the slag consisted mainly of Fe, Si and O while the Ca was minor. Elemental compositions obtained after analysis was used to identify the different phases in all the slag samples. The main phases identified were the same as those identified by the XRD analysis above except no phase with lithium was identified. No lithium was detected by SEM due to the design of the equipment as it uses beryllium planchets which prevent the detection of lithium.Leaching experiments were done on three slag samples (4, 5 and 6) that had lithium carbonate additions. Leaching was done for four hours using water, 1 molar HCl and 1 molar H2SO4 as leaching reagents at room temperature. Mixing was done using a magnetic stirrer. The recoveries obtained after leaching with water gave a lithium recovery of 0.4%. Leaching with HCl gave a recovery of 8.3% while a recovery of 9.4% was obtained after leaching with H2SO4.It can be concluded that the percentage of lithium recovered in this study was very low and therefore it would not be economically feasible. It can also be said that the recovery of lithium from the slag system studied in this work is very difficult because of the low recoveries obtained. It is recommended that test works be done on spent lithium ion batteries so as to get a better understanding of the possibilities of lithium recovery as spent lithium ion batteries contain other compounds unlike the ones investigated in this study.