Lithium batteries play a critical and indispensable role in our modern way of life, enabling portability and further miniaturization of several technologies that would otherwise be either stationary or simply not possible. As one of the most important technologies of the twenty-first century, our civilization enjoys the immense benefits it currently offers, and that it stands to offer in the decades to come. The existence of current systems can be traced back to a compromise made during the initial stages of lithium battery commercialization, when energy content had to be sacrificed for safety, reliability and performance, due to the instability of the lithium metal anode when used with flammable, liquid electrolytes. Since then, academia and industry have embarked on a decades long quest to overturn this compromise, and recover that which has been lost. Liquid electrolytes and graphite anodes are largely responsible for the great benefits of high power that lithium batteries afford us, but achieving greater energy densities, safety and performance will require different battery materials; the question is which ones, the answer to which is a task complicated by the delicate balance of many factors. Current battery research has sought to develop solid electrolytes to do away with the flammability and explosion issues tied with liquid electrolytes, either in the form of polymer or inorganic electrolytes. Polymer electrolytes are flexible and easy to manufacture, but suffer from low ambient temperature conductivities and performance, while inorganic electrolytes have high conductivities and mechanical moduli, but are brittle and suffer from poor interfacial properties, including limited thermodynamic stability against electrode materials, in many cases. The ipossibility of combining together polymer and inorganic electrolyte materials, to give hybrid electrolytes, is attractive, but issues such as component compatibility, ionic transport across interfaces within the material, and the issues inherited from the parent materials, have frustrated efforts to find a successful hybrid electrolyte. The lack of a clear, superior hybrid system prevents focused efforts from being centered around a narrow set of systems, making it more difficult to identify additional clues that can inform current known requirements for hybrid systems. In this present work, systematic efforts to characterize first the individual components of novel hybrid systems, and subsequently to characterize model systems and complete hybrid systems, are described.Chapter 1 provides a framework of principles governing lithium batteries, as well as the current issues plaguing lithium battery research, while Chapter 2 lists the materials, methods and equipment used in this work. Chapter 3 focuses on identifying a suitable organic polymer matrix, capable of covalent attachment, as well as characterizing plates of the inorganic electrolyte lithium aluminum silicon phosporus titanium oxide (LASPT). This includes thermal and electrochemical characterization, including plate-strip measurements and impedance spectroscopy. To the end of better understanding these materials' electrochemical properties, the approach of systematically investigating various equivalent circuits is developed, for the purpose of modeling impedance data. A suitable silane polymer matrix, capable of covalent attachment, is found and dubbed "Entry 02". The chief lesson of this chapter is that function and performance need to be balanced, which in this case translates to covalent moieties and electrochemical performance, respectively. Chapter 4 centers around electrochemical characterization of model systems, consisting of a plate of the inorganic electrolyte LASPT sandwiched between two layers of an organic electrolyte. The organic electrolytes used are liquid and gel electrolytes, as well as the aforementioned Entry 02; the liquid electrolytes are combinations of different amounts of tetraglyme and lithium bis(trifluoromethanesulfonimide) (G 4 and LiTFSI), while the gel electrolytes are combinations of 1:1 G 4 :LiTFSI (termed a solvated ionic liquid, or SIL) and methylcellulose (MC), dubbed "SIL/MC films". The plate of inorganic electrolyte is either bare, or has had a controlled amount of silica (SiO 2 ) deposited onto its faces by way of atomic layer deposition (ALD). Subsequently, as will be seen in the following chapter, this layer is intended to be deposited on the surface of powdered inorganic electrolyte, for the purpose of facilitating covalent attachment of Entry 02. Achievement of this goal requires sufficient understanding of resistance at the organic- inorganic interface, a question that is addressed in this chapter; indeed, a planar geometry configuration allows for a simpler approach to tackling this problem. A systematic study of impedance data by way of an equivalent circuit investigation is undertaken; the main finding of this chapter is that the SiO 2 layer is not detected as a separate impedance feature, instead affecting existing impedance features of the starting components. Additionally, the presence of SiO 2 on the surface of LASPT plates has a positive effect for cyclic voltammetry (CV) and plate-strip experiments, improving the profile of voltammograms in the former case, and lowering the voltage profile while also increasing experiment duration in the latter case. Chapter 5 is the completion of efforts to prepare and characterize polymer- ceramic hybrid electrolytes, by combining the powedered inorganic electrolyte lithium aluminum germanium phosphate (LAGP) with Entry 02. A systematic study impedance data by way of equivalent circuits reveals a distribution of equivalent circuits, which is believed to correspond to a distribution of conduction paths. Plate-strip experiments also indicate that the presence of SiO 2 deposited onto the surface of LAGP particles has a positive effect on both duration and voltage profile. Chapter 6 studies the thermal and electrochemical properties of the cocrystalline electrolyte (the term "cocrystal" will be used interchangeably with "cocrystalline electrolyte") composed of adiponitrile and lithium hexafluorophosphate, (ADN) 2 LiPF 6 . Thermal properties of other cocrystals are also studied for comparison, namely with adiponitrile lithium hexafluoroarsenate (ADN) 2 LiAsF 6 , and adiponitrile lithium hexafluoroantimonate (ADN) 2 LiSbF 6 . In all cases, the cocrystals are found to be formed by high temperature (180 °C) dissolution and crystallization, a reversible phenomenon observed for both cocrystals prepared beforehand, and for raw, stoichiometric mixtures of the cocrystals’ components. Electrochemical characterization of hybrids of LAGP powder and (ADN) 2 LiPF 6 , as well as of (ADN) 2 LiPF 6 , is also performed. For hybrids, it is found from plate-strip experiments that performance is worse than for samples using only (ADN) 2 LiPF 6 , while impedance data shows that overall conductivity drops as the thickness of SiO 2 deposited onto LAGP particles increases. Thermal characterization data reveals that it is possible to quantify the amount of excess ADN present in (ADN) 2 LiPF 6 samples; impedance data indicates that excess ADN improves conductivity of these samples. Conductivity is hypothesized to depend heavily on the presence of a liquid layer, which is present in greater quantities when excess ADN is used – a feature that is believed to be present to a lesser extent when stoichiometric amounts of ADN and LiPF 6 are used. Full cell testing of (ADN) 2 LiPF 6 and saturated solutions of LiPF 6 in ADN reveals that conditioning the cells beforehand is beneficial to long-term cycling, but harmful to short-term discharge rate (C-rate) tests. It is hypothesized that conditioning allows for the formation of an interphase that is conducive to lower current, long-term testing; this interphase however is believed to be resistive in nature, explaining the inferior performance in C-rate tests, when compared to C-rate tests where the conditioning step is omitted. Chapter 7 concludes this work, by providing an overview and an outlook on the results and lessons learned in this work, with the chief lesson being that covalent attachment of an organic component to an inorganic one is a feasible strategy for preparing hybrid electrolytes. / Chemistry

Battery Electric Vehicles (BEV) are gaining market share but still must overcome several engineering challenges related to the lithium-ion battery packs powering them. The batteries must be carefully managed to optimize safety and performance. The estimation of battery states, which cannot be measured directly, is an important part of battery management and remains an active area of research since small gains in estimation accuracy can help reduce cost and increase BEV range. This thesis presents several improvements to battery state estimation using different methods. Electrochemical Impedance Spectroscopy (EIS) is receiving increased attention from researchers as a method for state estimation and diagnostics for real-time applications. Due to battery relaxation behaviour, long rest times are commonly used before performing the EIS measurement. In this work, methods were developed to significantly shorten the required rest times, and a State of Health (SoH) estimation strategy was proposed by taking advantage of the relaxation effect as measured by EIS. This method was demonstrated to have an estimation error of below 1%. At low temperatures, the accuracy of the battery model becomes poor due to the non-linear battery response to current. By using an adaptive filter called the Interacting Multiple Model (IMM) filter, the next part of this work showed how to significantly improve low temperature State of Charge (SoC) estimation. Further reduction in estimation errors was achieved by pairing the IMM with the Smooth Variable Structure Filter (SVSF), for SoC estimation errors below 2%. The work presented in this thesis also includes the application of Deep Neural Networks (DNN) for SoC estimation from EIS data. Finally, an extensive aging study was conducted and an accelerated protocol was compared to a realistic drive cycle based protocol using EIS as a characterization tool. / Thesis / Doctor of Philosophy (PhD) / Replacing conventional gasoline/diesel powered cars with battery powered vehicles is part of a solution to the climate crisis. However, the initial costs paired with range anxiety stops many from switching to electric cars. Both cost and range are related to the battery pack. To achieve the best possible range for the lowest possible cost, battery packs must be carefully controlled by sophisticated algorithms. Unfortunately, battery range or health cannot be measured directly, but must be inferred through measurable indicators. This thesis explores battery behavior under different operating conditions and develops improved methods which can be used to determine battery health and/or range. A powerful method usually used only in laboratory settings is studied and improved to make it more suitable for implementation in electric cars. In this work it is used for accurate battery health determination. Furthermore, a strategy for improving battery range determination at low temperatures is also proposed.

Many sectors and industries are being pushed by policymakers and consumers towards an industrial transformation to become more sustainable. This in order to reduce the negative impact on the environment caused by the emissions of toxic substances and greenhouse gases, as well to promote more efficient use of resources. The transport sector and specifically the automotive industry is seen as one of the main actors within the climate debate due to their high environmental impact in terms of emissions. Therefore, authorities and customers are pushing automotive manufacturers to shift towards electric mobility. However, a rapid shift is not simple. The supply of raw materials needed to sustain the production of batteries does not meet the demand. In turn, causing shortages of some materials and heavily increasing their prices. This thesis addresses the supplier selection problem within a Swedish lithium-ion battery manufacturer with clients mainly in the automotive industry. The study has analyzed a set of relevant criteria to evaluate a supplier within the high-tech industry within a specific context. Furthermore, the study has determined whether differences exist between the importance of the criteria depending on the strategic profile of the material. The strategic profile depends on the profit impact and the supply risk of the material. In order to assess the importance weights of the criteria, the analytical hierarchy process (AHP) was used and interviews were conducted with purchasing experts in the industry. This study provides a new approach to the existing literature of supplier selection, by studying this process in an industry in which it has never been done and also by assessing the supplier selection by categorizing the materials by their strategic profile, an approach that has not been studied in literature until the moment. Results show that the importance of some of the supplier selection criteria vary widely between the strategic profile of the materials, while the importance of other criteria remain the same. In addition, the study has also determined that the importance of the criteria vary also within the supplier selection process, having different importance levels at different steps. Finally, the results show that some criteria of a certain criticality represent a go-no go gate in the selection process. The conclusions are that the supplier selection process within the battery industry cannot be regarded as a homogenous process and that supplier selection criteria vary with the strategic importance of the material. Thus, suppliers must be assessed with different criteria importance weights when using a tool such as the AHP to perform supplier selection. Additionally, the critical criteria for each material must be determined prior to use the tool. / Politiker och konsumenter ställer allt högre krav på industrin att genomföra åtgärder för att bli mer hållbara, exempelvis genom att minska utsläpp av giftiga ämnen och växthusgaser samt ett mer effektivt resursanvändande. Transportsektorn och bilindustrin är särskilt utpekade inom miljödebatten på grund av deras höga miljöpåverkan och stora mängder av utsläpp. Biltillverkarna drivs därför mot en industriell omvandling där förnybara bränslen ska ersätta fossila bränslen. Övergången till eldrivna fordon är en långsam och komplicerad process där flödeskedjan för effektiv tillverkning av bilbatterier fortfarande är under utveckling. Tillgången på vissa råmaterial som behövs för produktionen av batterier räcker inte för att mätta efterfrågan vilket drar upp prisnivån. Samtidigt etablerar sig många nya leverantörer av råmaterial vars varierande kvalitet och pålitlighet skapar ytterligare utmaningar hos batteritillverkarna. Studien behandlar urvalsprocessen vid inköp av material hos en svensk litium-jonbatteritillverkare med kunder främst inom bilindustrin. Urvalskriterier för att utvärdera leverantörer inom högteknologisk industri analyserats. Därtill har det utretts om skillnader existerar mellan kriteriernas betydelse beroende på råvarornas strategiska profil. Den strategiska profilen beräknas genom dess påverkan på produktens slutkostnad tillsammans med risken för avbrott i försörjningskedjan. Metoden Analytic Hierarchy Process (AHP) används för att bedöma dessa kriteriers betydelse. Därtill har intervjuer genomförts med branch-experter för att ge fördjupad insikt i kriteriernas betydelse. Studien ger två huvudsakliga bidrag till den akademiska litteraturen. Först och främst utvärderas urvalskriterierna, som identifierats i litteraturstudien, inom en industrisektor där de inte prövats tidigare. Urvalskriterierna för leverantörsval appliceras dessutom specifikt för råmaterial av olika strategisk profil för att studera i vilken utsträckning de skiljer sig åt. Även denna ansats är tidigare oprövad inom den akademiska litteraturen. Resultaten visar att vikten av vissa kriterier varierar i hög utsträckning mellan material av olika strategisk profil, medan andra kriterier är näst intill opåverkade. Studien har dessutom fastställt att betydelsen av vissa kriterier varierar mellan olika steg i urvalsprocessen. Somliga kriterier representerar en kritisk punkt i urvalsprocessen och utesluter de leverantörer som inte kan leverera upp till en miniminivå. Studiens slutsas är att urvalsprocessen vid val av leverantör inom batteribranschen inte kan ses som en homogen process då urvalskriterierna varierar med materialets strategiska betydelse. Råmaterialens strategiska profil måste alltså tas i beaktning vid användning av ett urvalsverktyg som AHP. De kritiska kriterier som leverantören måste leva upp till måste dessutom fastställas innan verktyget kan tas i bruk.

Due to legislative pressure on a global, European and Swedish level the heavy-duty transportation sector needs to drastically reduce its emissions. One potential pathway forward for the heavy-duty transportation sector is that of electrification, which would require novel infrastructure to be established in the form of stationary charging or dynamic charging through what is often called electric road systems (ERS). The aim of this thesis has been to investigate how developments in battery technology impacts the potential electrification of heavy-duty transportation in Sweden. The starting point is from the perspective of battery technology and the resulting impact that battery technology has on the provision of charging infrastructure. In order to analyse the relation between these parameters the market developments of lithium-ion batteries were explored and an empirical study of the likely stakeholders of an electrified heavy-duty transportation system was conducted. The study finds that battery technology has a substantial momentum and several stakeholders view the electrification of heavy-duty transportation as the most cost-efficient solution in the long-term. There is however a consensus that battery development has not yet progressed to a stage where the electrification of heavy-duty transportation is financially or technically viable. Developments in battery technology affect the prospects for stationary charging provision and ERS (i.e. dynamic charging) differently, with stationary charging being more dependent on positive developments. The relation between developments in battery technology and ERS is more complex as its deployment is not only dependent on market developments but is also highly dependent on decisive actions by policy makers. Developments in battery technology could however affect both alternatives positively in the long-term, as a sustained positive battery development will make fully electric heavy-duty trucks an attractive option for the market to pursue. Once a common belief in the electrification of heavy-duty transportation has been established the main issue described by stakeholders, ensuring a long-term positive business case, could therefore be achieved by both alternatives. The study concludes that for an electrification of heavy-duty transportation to be financially sustainable in the long-term, continued positive battery developments are a prerequisite. / Till följd av lagstiftningskrav på en global, europeisk och svensk nivå så måste tunga vägtransporter drastiskt minska sina utsläpp. En möjlig utveckling för tunga vägtransporter kan vara elektrifiering vilket skulle kräva en etablering av ny infrastruktur, antingen i form av stationära laddstationer, eller i form av elvägar. Syftet med denna uppsats har varit att utreda hur batteriutvecklingen påverkar förutsättningarna för att tunga vägtransporter i Sverige skulle kunna elektrifieras. Utgångspunkten har varit utifrån perspektivet av batteriteknologi och den påverkan som batteriteknologin har på tillhandahållandet av laddinfrastruktur. För att analysera relationen mellan dessa parametrar så har marknadsutvecklingen för litium-jon batterier utretts och en empirisk studie med de aktörer som troligen skulle vara delaktiga i ett elektrifierat transportsystem har utförts. Studiens slutsatser är att batteriteknologin har ett betydande momentum och att flera aktörer på sikt ser elektrifieringen av tunga vägtransporter som den mest kostnadseffektiva lösningen. Det råder dock en konsensus om att batteriutvecklingen ännu inte har kommit långt nog för att elektrifieringen av tunga vägtransporter ska vara tekniskt eller ekonomiskt gångbar. Batteriutvecklingen påverkar utsikterna för tillhandahållandet av stationära laddstationer och elvägar på olika sätt, där stationära laddstationer är mer beroende av en positiv batteriutveckling. Relationen mellan batteriutvecklingen och elvägar är mer komplex då etableringen av elvägar inte bara är beroende av marknadsförhållanden utan även är avhängig på ett starkt politiskt stöd. Batteriutvecklingen kan dock ha en positiv påverkan på båda dessa alternativ på lång sikt, då en ihållande positiv batteriutveckling skulle göra helelektriska tunga lastbilar till ett attraktivt alternativ för marknaden att eftersträva. När en gemensam övertygelse om att elektrifieringen av tunga vägtransporter är den optimala vägen framåt har uppnåtts så kan det huvudsakliga problemet som aktörer beskriver, upprättandet av långsiktigt hållbara affärsmodeller, uppnås av båda alternativen. Studien drar slutsatsen att för att en elektrifiering av tunga vägtransporter ska vara ekonomiskt hållbar på sikt så är en fortsatt positiv batteriutveckling en förutsättning.

When an anode electrode potential is larger than the lowest unoccupied molecular orbital (LUMO) of the electrolyte, Li-ions and electrolyte molecules will participate in reduction reactions on the anode surface and form a solid electrolyte interface (SEI) layer. Active Li-ion consumption in the formation reactions is the main source of capacity loss (>50) and ageing in Li-ion batteries (LIBs). Due to the fast-occurring and complex nature of the electrochemical processes, conventional experimental techniques are not a feasible approach for capturing and characterizing the SEI formation phenomenon. The lack of experimental data and consequently the absence of potential parameters for crystal structures in this layer makes molecular dynamics~(MD) simulations inapplicable to it. Also, due to the multi-component multi-layer structure of the SEI, the smallest system representing an SEI layer is too large for employing the principles of quantum mechanics~(QM), that traditionally work with much smaller system sizes. Addressing this, this thesis presents a novel computational framework for coupling QM and MD calculations to simulate a system with the size limits of MD simulations independent of the experimental data. The QM evaluates sub-atomic properties such as energy barriers against diffusion and employs seven new algorithms to estimate potential parameters as the input of the MD simulations. Then MD simulations forecast SEI's properties including density, Young's Modules, Poisson's Ratio, thermal conductivity, and diffusion coefficient mechanisms. The output of the QM and MD calculations are employed to develop two macro-scale mathematical models for predicting battery ageing and battery performance, incorporating the impact of the SEI layer in addition to the cathode, anode, and separator parts. Finally, the results obtained have been validated with respect to the experimental data in different operational conditions. / Thesis / Doctor of Philosophy (PhD) / The limited lifespan of expensive batteries is the main obstacle to electrification of the transport sector, despite its necessity for addressing the current environmental issues. Li+/electrolyte reduction on the electrode surface is responsible for more than 50% of capacity loss and the consequent ageing is a complex and fast-occurring phenomenon (few ns) that cannot be easily resolved using conventional experimental and computational techniques. This thesis presents the development of some computational frameworks and demonstrates their employment to investigate this phenomenon from a multi-scale perspective, i.e., from a few electrons to an entire battery length scale, with the operating cycles ranging from a few ps to several months, employing Quantum Mechanics, Molecular Dynamics, and Macro-Scale Modeling. The frameworks have been successfully validated with respect to experimental data from the literature and have been applied successfully to highlight the parameters that impact ageing in batteries. The findings presented in this thesis can be used as the base for further research on next-gen durable batteries with liquid and solid-state electrolytes.

Thesis (Ph.D. (Physics)) -- University of Limpopo, 2017 / Density functional theory (DFT) study is employed in order to investigate the surfaces of, β-MnO2, β-TiO2 and β-VO2 (β-MO2) which act as catalysts in Li/Na-air batteries. Adsorption and co-adsorption of metal (Li/Na) and oxygen on (110) β-MO2 surface is investigated, which is important in the discharging and charging of Li/Na– air batteries. Due of the size of the supercell, and assuming that oxygen atoms occupy bulk-like positions around the surface metal atoms, only five values of (gamma) Γ are possible if constraint to a maximum of 1 monolayer (ML) of adatoms or vacancies: Γ= 0 surface is the stoichiometric surface, Γ= 1, 2 are the partially and totally oxidised surfaces, and Γ=-1, -2 are the partially and totally reduced surfaces. The manganyl, titanyl and vanadyl terminated surface is not the only surface that can be formed with Γ= +2. Oxygen can be adsorbed also as peroxo species (O2)2-, with less electron transfer from the surface vanadium atoms to the adatoms than in the case of manganyl and titanyl formation. The redox properties of the (110) surfaces are investigated by calculating the relative surface free energies of the non-stoichiometric compositions as a function of oxygen chemical potential. Increasing the temperature and lowering the pressure (i.e. more reducing conditions) we find the stoichiometric surface reduces first partially and then entirely at higher temperatures. The lithium orientation between two bridging oxygen and in-plane oxygen (bbi) orientation is much more stable for the three metal oxides, thus lithium generally prefers to adsorb where it will be triply coordinated to two bridging oxygens and one in-plane oxygen atom. However, sodium prefers to orientate itself on the bridging oxygen on the surface, but a triple coordination on sodium is also favourable. Oxygen adsorption on Li/MO2 was simulated and it was found that in all ii the metal oxides (MnO2, TiO2 and VO2) the most stable orientation is the dissociated composition where there is an oxygen atom on the “bulk-like” positions on top of each of the M cations. The surface lithium peroxide for MO2 simulated produces clusters with oxygen - oxygen bond lengths that are comparable to the calculated bulk and monomer discharge products reported in literature. Adsorption of oxygen on Na/MO2 was investigated and it was observed that the catalysts used encourage formation of the discharge product reported in literature, i.e. NaO2. The surface NaO2 appears to have comparable bond lengths to the calculated bulk and monomer NaO2. / National Research Foundation, South African Research Chair Initiative of the Department of Science Technology and Department of Energy storage Programme

Indiana University-Purdue University Indianapolis (IUPUI) / Lithium-ion batteries are widely used for portable electronics due to high energy density, mature processing technology and reduced cost. However, their applications are somewhat limited by safety concerns. The lithium-ion battery users will take risks in burn or explosion which results from some internal components failure. So, a practical method is required urgently to find out the failures in early time. In this thesis, a new method based on temperature difference between internal point and surface (TDIS) of the battery is developed to detect the thermal failure especially the thermal runaway in early time. A lumped simple thermal model of a lithium-ion battery is developed based on TDIS. Heat transfer coefficients and heat capacity are determined from simultaneous measurements of the surface temperature and the internal temperature in cyclic constant current charging/discharging test. A look-up table of heating power in lithium ion battery is developed based on the lumped model and cyclic charging/discharging experimental results in normal operating condition. A failure detector is also built based on TDIS and reference heating power curve from the look-up table to detect aberrant heating power and bad parameters in transfer function of the lumped model. The TDIS method and TDIS detector is validated to be effective in thermal runaway detection in a thermal runway experiment. In the validation of thermal runway test, the system can find the abnormal heat generation before thermal runaway happens by detecting both abnormal heating power generation and parameter change in transfer function of thermal model of lithium ion batteries. The result of validation is compatible with the expectation of detector design. A simple and applicable detector is developed for lithium ion battery catastrophic failure detection.

No description available.

Thesis (Ph.D. (Physics)) -- University of Limpopo, 2020 / This work presents a computational modelling workflow that uniquely combines several techniques, proposed as a means for studying and designing high-energy-density electrodes for the next-generation of rechargeable batteries within the era of the fourth industrial revolution (4IR). The Self-Consistent Charge Density Functional-based Tight Binding (SCC-DFTB) parameterisation scheme for the Li-Si and Na-Si systems is presented. By using the Li-Si system, a procedure for developing the Slater-Koster based potentials is shown. Using lessons learned from the Li-Si framework, the parameterisation of the Na-Si is reported. The Li-Si SCC-DFTB parameter set has been developed to handle environments that consist of Si-Si, Li-Si and Li-Li interactions; and the Na-Si SCC DFTB parameter set is developed for Na-Na, Na-Si, and Si-Si interactions. Validations and applications of the developed sets are illustrated and discussed. By calculating equilibrium lattice constants, the Li-Si set is shown to be compatible with various phases in the crystalline Li-Si system. The results were generally within a margin of less than 8% difference, with some values such as that of the cubic Li22Si5 being in agreement with experiments to within 1%. The volume expansion of Si as a function of Li insertion was successfully modelled via the Li-Si SCC-DFTB parameter set. It was shown that Si gradually expands in volume from 53.6% for the LiSi phase composed of 50 atm % Li, to 261.57% for Li15Si4 with 78.95 atm % Li, and eventually shoots over 300% for the Li22Si5 phase with the expansion at 316.45%, which agrees with experiments. Furthermore, the ability of the Li-Si SCC-DFTB parameter set to model the mechanical properties of Si is evaluated by calculating the mechanical properties of pristine cubic Si. The parameter set was able to produce the mechanical properties of Si, which agree with experiments to within 6%. The SCC-DFTB parameter set was then used to model the volume expansion of amorphous silicon (a-Si) as a result of lithiation within concentrations ranging from 33 – 50 atm % Li. Consistent with experiments, the a-Si was found to marginally expand in a linear form with increase in Li content. a-Si was observed to exhibit a lower expansion compared to c-Si. Additionally, the structural stability of the amorphous Li-Si alloys was examined, and observations agree with experiments.vi The Na-Si SCC-DFTB parameter set produced equilibrium lattice parameters that agree with experiments to within 4% for reference structures, and the transferability was tested on three Na-Si clathrate compounds (i.e. the Pm-3n Na8Si46, the Cmcm NaSi6 and Fd-3m Na24Si136). By employing the approach used when lithiating Si, the sodiation of crystalline silicon (c-Si) was modelled. It was predicted that c-Si expands by over 400% at 77 atm% Na and shoots above 500% for concentrations exceeding 80 atm% of Na. By comparing how c-Si expands as a result of lithiation to the expansion consequent to sodiation for concentrations ranging from 66.6 – 81.4 atm%, c-Si is shown to be unsuitable for Na-ion batteries. As a test, the ability of the developed Na-Si SCC DFTB parameter set to handle large and complex geometries was shown by modelling the expansion of a-Si at 33 atm% Na. It was deduced that a-Si would be more preferable for Na-ion batteries since at 33 atm% Na, a-Si expanded a lot less than when c-Si was used. Using the Li-Si and the Na-Si SCC-DFTB parameter sets, it was noted that amorphisation appears to lower the magnitude by which Si expands, therefore agreeing with experiments in that amorphous structures are reported to exhibit a buffering effect towards volume expansion. The material space for the Li-Si alloy system is explored through crystal structure predictions conducted via a machine learning powered cluster expansion (CE). Using the FCC and BCC – based parent lattice in the grid search, 12 thermodynamically stable Li-Si alloys were predicted by the genetic algorithm. Viz. the trigonal Li4Si (R-3m), tetragonal Li4Si (I4/m), tetragonal Li3Si (I4/mmm), cubic Li3Si (Fm-3m), monoclinic Li2Si3 (C2/m), trigonal Li2Si (P-3m1), tetragonal LiSi (P4/mmm), trigonal LiSi2 (P-2m1), monoclinic LiSi3 (P2/m), cubic LiSi3 (Pm-3m), tetragonal LiSi4 (I4/m) and monoclinic LiSi4 (C2/m). The structural stabilities of the predicted Li-Si alloys are further studied. With focus on pressure, the thermodynamic conditions under which the Li-rich phase, Li4Si (R 3m), would be stable are tested. Li4Si (R-3m) was subjected to pressures during geometry optimization and found to globally maintain its structural stability within the range 0 – 25GPa. Hence, Li4Si was predicted to be a low pressure phase. In studying the PDOS, the Li4Si (I4/m) was noted to be more stable around 40GPa and vii 45GPa, which is consistent with the prediction made from other works, wherein intelligence-based techniques were used. A test for exploring the Na-Si material space was done using insights acquired from the Li-Si framework. Three thermodynamically stable Na-Si (i.e. the I4/mmm Na3Si, P4/nmm NaSi and Immm NaSi2) were predicted. Using the Na-Si SCC-DFTB parameter set, a correlation of the total DOS in the vicinity of the Fermi level (Ef) with the structural stability of the three Na-Si alloys is done. NaSi (P4/nmm) was shown to be unstable at 0GPa, NaSi2 (Immm) is found to be stable, and the Na-rich Na3Si exhibited metastability. The stability of Na3Si was seen to improve when external pressure ranging from 2.5 – 25GPa was applied; hence, suggesting Na3Si (I4/mmm) to be a high-pressure phase. Furthermore, expanding on the groundwork laid from the Li-Si and Na-Si CE, the Mg-Si system was tested to illustrate that the approach can be used to rapidly screen for new materials. The ground-state crystal structure search predicted 4 thermodynamically stable Mg-Si alloys. Viz. Mg3Si (Pm-3m), MgSi (P4/mmm), MgSi2 (Immm) and MgSi3 (Pmmm). Lastly, to highlight the power of combining various computational techniques to advance material discovery and design, a framework linking SCC-DFTB and CE is illustrated. Candidate electrode materials with nano-architectural features were simulated by designing nanospheres comprised of more than 500 atoms, using the predicted Li-Si and Na-Si crystal structures. The stability of the nanospheres was examined using SCC-DFTB parameters developed herein. The workflow presented in this work paves the way for rapid material discovery, which is sought for in the era of the fourth industrial revolution. / National Cyber Infrastructure System: Center for High-Performance Computing (NICIS-CHPC) for computing resources, the National Research Foundation (NRF) and the University of Limpopo

Metal-based high entropy oxides are considered promising electrode materials for use in Li- ion batteries. In this work, the most widely studied high entropy oxide Mg0.2Ni0.2Cu0.2Co0.2Zn0.2O (M-HEO) with rock salt structure was successfully synthesized by Modified Pechini synthesis, characterized by X-ray diffraction analysis, and investigated as anode active material (negative electrode) in a coin cell. M-HEO has the concept of entropy stabilisation of crystal structure in oxide system with the configurational entropy value of 1,6R which confirmed that M-HEO classified as high entropy oxide.  To test the electrochemical performance, full cells comprising M-HEO as anode, lithium manganese oxide (LMO) as cathode together with ionic liquid electrolyte were assembled to explore their potential for practical applications. The electrochemical cycling performance was studied by two electrochemical experiments which are three-electrode cyclic voltammetry and galvanostatic charge/discharge. The cyclic voltammetry measurement was used to determine the behaviour of the system such as potential window and scan rate, while galvanostatic charge/discharge was used to determine the performance of the battery over time by applying constant current.  The results demonstrate that high entropy oxide possess a stable structure. This points out the direction for the preparation of M-HEOs with stable structure and excellent performance and provides a promising candidate for anode materials for LIBs. / Metallbaserade högentropioxider anses vara lämpliga för användning av elektrodmaterial för litium-jon batterier. I detta arbete syntetiserades den första högentropioxiden Mg0.2Ni0.2Cu0.2Co0.2Zn0.2O (M-HEO) som har stensaltstruktur genom Modifierad Pechini- syntesmetod, karakteriserad av röntgendiffraktionsanalys och undersöktes som aktivt material i den negativa elektroden. M-HEO har konceptet av entropistabilisering av kristallstrukturen i oxidsystem som har det konfigurerade entropivärdet av 1,6R. Detta bekräftade att M-HEO klassificerades som högentropioxid.  För att testa den elektrokemiska prestandan, användes fullceller bestående av M-HEO som anod, litiummanganoxid (LMO) som katod tillsammans med jonisk flytande elektrolyt. Detta gjordes för att undersöka M-HEO potentiella praktiska tillämpningar. Den elektrokemiska cyklingsprestandan studerades genom två elektrokemiska experiment, cyklisk voltammetri med tre-elektroder och galvanostatisk laddning/urladdning med knapp-celler. Den cykliska voltammetri mätningen användes för att bestämma vart i systemet sker redox reaktion för att sedan kunna identifiera på vilka potentialintervall samt skanningshastighet, medan galvanostatisk laddning/urladdning användes för att bestämma batteriets prestanda över tid genom att applicera konstant ström. Resultaten visar sig att hög entropi oxider har en stabil stensaltstruktur. Detta bidrar till att M-HEO som har en stabil struktur kan vara ett lämpligt anodmaterial i litium-jon batterier.