Si-based anodes have recently received considerable attention for use in Li-ion batteries, due to their extremely high specific capacity - an order of magnitude beyond that offered by conventional graphite anode materials. However, during the lithiation process, Si-based anodes undergo extreme increases in volume, potentially by more than 300 %. The stresses produced within the electrode by these volume changes can damage the electrode binder, the active Si particles and the solid electrolyte interphase (SEI), causing the electrode to rapidly fail and lose capacity. These problems can be overcome by producing new anode materials incorporating both Si and C, which may offer a favorable combination of the best properties of both materials, and which can be designed with internal porosity, thereby buffering the high strains produced during battery charge and discharge with minimal overall volume changes. However, in order to develop useful anode materials, we must gain a thorough understanding of the structural, microstructural and chemical changes occurring within the electrode during the lithiation and delithiation process, and we must develop new processes for synthesizing composite anode particles which can survive the extreme strains produced during lithium intercalation of Si and exhibit no volume changes in spite of the volume changes in Si. In this work we have developed several novel synthesis processes for producing internally porous Si-C nanocomposite anode materials for Li-ion batteries. These nanocomposites possess excellent specific capacity, Coulombic efficiency, cycle lifetime, and rate capability. We have also investigated the influence of a range of different parameters on the electrochemical performance of these materials, including pore size and shape, carbon and silicon film thickness and microstructure, and binder chemistry.

In the early 1970s, research carried out on rechargeable lithium batteries at the Exxon Laboratories in the US established that lithium ions can be intercalated electrochemically into certain layered transition-metal sulphides, the most promising being titanium disulphide. Stemming from this discovery for titanium disulphide, there has been increased interest on lithium-ion intercalation compounds for application in rechargeable batteries. The first rechargeable lithium cell was commercialized in late 1980s by Moli Energy Corporation in Canada. The cell comprised a spirally wound lithium foil as the anode, a separator and MoS2 as the cathode. The cell had a nominal voltage of 1.8 V and an attractive value of specific energy, which was 2 to 3 times greater than either lead-acid or nickel-cadmium cells. However, the battery was withdrawn from the market after safety problems were experienced. This paved way for the discovery of lithium-ion battery. The origin of lithium-ion battery lies in the discovery that Li+-ions can be reversibly intercalated within or deintercalated from the van der Walls gap between graphene sheets of carbon materials at a potential close to the Li/Li+ electrode. Thus, lithium metal is replaced by carbon as the anode material for rechargeable lithium-ion batteries, and the problems associated with metallic lithium mitigated. Complimentary investigations on intercalation compounds based on transition metals resulted in establishing LiCoO2 and LiNiO2 as promising cathode materials. By employing aforesaid intercalation materials, namely carbon and LiCoO2 respectively, as negative and positive electrodes in a non-aqueous lithium-salt electrolyte, a Li-ion cell with a voltage value of about 3.5 V resulted. These findings led to a novel rechargeable battery technology. Lithium-ion batteries were first introduced commercially in 1991 by the Sony Corporation in Japan. Other Japanese manufacturers soon entered the market, followed closely by American and European companies. The subsequent growth in sales of the batteries was truly phenomenal. Beginning from 1991, the lithium-ion battery market has grown from an R&D interest to sales of over 400 million units in 1999. The global market value for lithium-ion batteries at original equipment manufacturer level was estimated to be $1.86 billion in 2000. By 2006, the market is expected to grow to over 1.2 billion units with value of over $4 billion, while the average unit price is expected to fall. Initially, realizable specific energy of commercial Li-ion battery was only about 120 Wh kg-1. However, with continuing improvements in various cell components, present day Li-ion batteries can provide a specific energy density of about 200 Wh kg-1. With the ‘holy grail’ far to be realized, the current R&D efforts are focussed on furthering the specific energy of lithium-ion batteries in conjunction with safety, environmental compatibility, and cost effectiveness. In the Li-ion cell, all of its electrochemical constituents, namely anode, cathode and electrolyte are central to its performance. This thesis describes some novel studies on cathode and anode materials for lithium-ion Batteries.

The physics of transition metal oxides is controlled by the combination and competition of several degrees of freedom, in particular the charge, the spin and the orbital state of the electrons. One important parameter responsible for the physical properties is the density of charge carriers which determines the oxidization state of the transition metal ions. The central objective in this work is the study of transition metal oxides in which the charge carrier density is adjusted and controlled via lithium intercalation/deintercalation using electrochemical methods. Lithium exchange can be achieved with a high degree of accuracy by electrochemical methods. The magnetic properties of various intermediate compounds are studied. Among the materials under study the mixed valent vanadium-oxide multiwall nanotubes represent a potentially technologically relevant material for lithium-ion batteries. Upon electron doping of VOx-NTs, the data confirm a higher number of magnetic V4+ sites. Interestingly, room temperature ferromagnetism evolves after electrochemical intercalation of Li, making VOx-NTs a novel type of self-assembled nanoscaled ferromagnets. The high temperature ferromagnetism was attributed to formation of nanosize interacting ferromagnetic spin clusters around the intercalated Li ions. This behavior was established by a complex experimental study with three different local spin probe techniques, namely, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and muon spin relaxation spectroscopies. Sr2CuO2Br2 was another compound studied in this work. The material exhibits CuO4 layers isostructural to the hole-doped high-Tc superconductor La2-xSr2CuO4. Electron doping is realized by Li-intercalation and superconductivity was found below 9K. Electrochemical treatment hence allows the possibility of studying the electronic phase diagram of LixSr2CuO2Br2, a new electron doped superconductor. The effect of electrochemical lithium doping on the magnetic properties was also studied in tunnel-like alpha-MnO2 nanostructures. Upon lithium intercalation, Mn4+ present in alpha-MnO2 will be reduced to Mn3+, resulting in a Mn mixed valency in this compound. The mixed valency and different possible interactions arising between magnetic spins give a complexity to the magnetic properties of doped alpha-MnO2.

In this paper, we report that various kinds of active sites on graphite surface including active hydrophilic sites markedly affect the electrochemical performance of graphite anodes for lithium ion batteries under different humidity conditions. After depositing metals such as Ag and Cu by immersing and heat-treating, these active sites on the graphite surface were removed or covered and its electrochemical performance under the high humidity conditions was markedly improved. This suggests that lithium ion batteries can be assembled under less strict conditions and that it provides a valuable direction to lower the manufacturing cost for lithium ion batteries.

Magnetic properties of powders, thin films and single crystals have been investigated using magnetometry methods. This thesis provides analysis and conclusions that are supported by the results obtained from spectroscopic and diffraction measurements as well as from theoretical calculations. First, the magnetic behavior of transition metal (TM) doped ZnO with respect to doping, growth conditions and post annealing has been studied. Our findings indicate that the magnetic behavior stems from small clusters or precipitates of the dopant, with ferromagnetic or antiferromagnetic interactions. At the lowest dopant concentrations, the estimated cluster sizes are too small for high resolution imaging. Still, the clusters may be sufficiently large to generate a finite spontaneous magnetization even at room temperature and could easily be misinterpreted as an intrinsic ferromagnetic state of the TM:ZnO compound. Second, influence of lattice strain on both magnetic moment and anisotropy has been investigated for epitaxial MnAs thin films grown on GaAs substrates. The obtained magnetic moments and anisotropy values are higher than for bulk MnAs. The enhanced values are caused by highly strained local areas that have a stronger dependence on the in-plane axis strain than out-of plane axis strain. Finally, spin glass behavior in Li-layered oxides, used for battery applications, and a double perovskite material has been investigated. For both Li(NiCoMn)O2 and (Sr,La)MnWO6, a mixed-valence of one of the transition metal ions creates competing ferromagnetic and antiferromagnetic interactions resulting in a low temperature three-dimensional (3D) spin glass state. Additionally, Li(NiCoMn)O2 with large cationic mixing exhibits a percolating ferrimagnetic spin order in the high temperature region and coexists with a two-dimensional (2D) frustrated spin state in the mid temperature region. This is one of the rare observations where a dimensional crossover from 2D to 3D spin frustration appears in a reentrant material. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 720

Recent carbon allotropes such as carbon nanotubes (CNTs), fullerenes (C60s) and graphene have attracted great interests in both science and engineering due to their unique properties such as excellent electrical and mechanical properties as well as its vast surface area, and have led to many commercial applications. Especially, CNTs have been considered to be one of the promising candidates in the Li ion battery system because of its outstanding properties. However, the experimental results in the pristine CNT system have shown just slight improvement than original graphitic carbon material, which has been attributed to the weak adsorption of Li on CNTs. In this study, we investigated two types of CNT-C60 hybrid system consisting of CNTs and C60s to improve Li adsorption capabilities and predict its performance through quantum mechanical (QM) computations. First, we investigated adsorption energy of lithium (Li) on dilute CNT-C60 hybrid and CNT-C60 nanobud system as well as various electronic properties such as band structure, density of states (DOS), molecular orbital and charge distribution. Then, we expanded our interest to the more realistic condensed structure of CNT-C60 hybrid and nanobud system to examine actual electrochemical characteristics. The study of the condensed structure has been expanded to the very unique CNT-C60 nano-network system and examined mechanical strength as well as electronic properties. Finally, Li adsorption on other carbon allotropes system such as graphene-C60 hybrid and graphene-C60 bud system was investigated in order to provide fundamental understanding of electronic interaction between carbon allotrope and effect of Li adsorption.

This thesis investigates novel algorithms for enabling the use of first-principle electrochemical models for battery monitoring and control in advanced battery management systems (BMSs). Specifically, the fast solution and state estimation of a high-fidelity spatially resolved thermal-electrochemical lithium-ion battery model commonly referred to as the pseudo two-dimensional (P2D) model are investigated. The partial-differential algebraic equations (PDAEs) constituting the model are spatially discretised using Chebyshev orthogonal collocation enabling fast and accurate simulations up to high C-rates. This implementation of the P2D model is then used in combination with an extended Kalman filter (EKF) algorithm modified for differential-algebraic equations (DAEs) to estimate the states of the model, e.g. lithium concentrations, overpotential. The state estimation algorithm is able to rapidly recover the model states from current, voltage and temperature measurements. Results show that the error on the state estimate falls below 1% in less than 200s despite a 30% error on battery initial state-of-charge (SoC) and additive measurement noise with 10mV and 0.5°C standard deviations. The parameter accuracy of such first-principle models is of utmost importance for the trustworthy estimation of internal battery electrochemical states. Therefore, the identifiability of the simpler single particle (SP) electrochemical model is investigated both in principle and in practice. Grouping parameters and partially non-dimensionalising the SP model equations in order to understand the maximum expected degrees of freedom in the problem reveals that there are only six unique parameters in the SP model. The structural identifiability is then examined by asking whether the transfer function of the linearised SP model is unique. It is found that the model is unique provided that the electrode open circuit voltage curves have a non-zero gradient, the parameters are ordered, and that the behaviour of the kinetics of each electrode is lumped together into a single parameter which is the charge transfer resistance. The practical estimation of the SP model parameters from frequency-domain experimental data obtained by electrochemical impedance spectroscopy (EIS) is then investigated and shows that estimation at a single SoC is insufficient to obtain satisfactory results and EIS data at multiple SoCs must be combined.

Two novel lithium host materials were investigated using structural and electrochemical analysis; the cathode material Li₂CoSiO₄ and the LiMO₂ class of anodes (where M is a transition metal ion). Li₂CoSiO₄ materials were produced utilising a combination of solid state and hydrothermal synthesis conditions. Three Li₂CoSiO₄ polymorphs were synthesised; β[subscript(I)], β[subscript(II)] and γ₀. The Li₂CoSiO₄ polymorphs formed structures based around a distorted Li₃PO₄ structure. The β[subscript(II)] material was indexed to a Pmn2₁ space group, the β[subscript(I)] polymorph to Pbn2₁ and the γ₀ material was indexed to the P2₁/n space group. A varying degree of cation mixing between lithium and cobalt sites was observed across the polymorphs. The β[subscript(II)] polymorph produced 210mAh/g of capacity on first charge, with a first discharge capacity of 67mAh/g. It was found that the β[subscript(I)] material converted to the β[subscript(II)] polymorph during first charge. The γ₀ polymorph showed almost negligible electrochemical performance. Capacity retention of all polymorphs was poor, diminishing significantly by the tenth cycle. The effect of mechanical milling and carbon coating upon β[subscript(II)], β[subscript(I)] and γ₀ materials was also investigated. Various Li[subscript(1+x)]V[subscript(1-x)]O₂ materials (where 0≤X≤0.2) were produced through solid state synthesis. LiVO₂ was found to convert to Li₂VO₂ on discharge, this process was found to be strongly dependent on the amount of excess lithium in the system. The Li₁.₀₈V₀.₉₂O₂ material had the highest first discharge capacity at 310mAh/g. It was found that the initial discharge consisted of several distinct electrochemical processes, connected by a complicated relationship, with significant irreversible capacity on first discharge. Several other LiMO₂ systems were investigated for their ability to convert to layered Li₂MO₂ structures on low voltage discharge. While LiCoO₂ failed to convert to a Li₂CoO₂ structure, LiMn₀.₅Ni₀.₅O₂ underwent an addition type reaction to form Li₂Mn₀.₅Ni₀.₅O₂. A previously unknown Li₂Ni[subscript(X)]Co[subscript(1-X)]O₂ structure was observed, identified during the discharge of LiNi₀.₃₃Co₀.₆₆O₂.

Doctor of Philosophy / Department of Chemistry / Jun Li / Nanostructured electrode materials for electrochemical energy storage systems have been shown to improve both rate performance and capacity retention, while allowing considerably longer cycling lifetime. The nano-architectures provide enhanced kinetics by means of larger surface area, higher porosity, better material interconnectivity, shorter diffusion lengths, and overall mechanical stability. Meanwhile, active materials that once were excluded from use due to bulk property issues are now being examined in new nanoarchitecture. Silicon was such a material, desired for its large lithium-ion storage capacity of 4,200 mAh g[superscript]-1 and low redox potential of 0.4 V vs. Li/Li[superscript]+; however, a ~300% volume expansion and increased resistivity upon lithiation limited its broader applications. In the first study, the silicon-coated vertically aligned carbon nanofiber (VACNF) array presents a unique core-shell nanowire (NW) architecture that demonstrates both good capacity and high rate performance. In follow-up, the Si-VACNFs NW electrode demonstrates enhanced power rate capabilities as it shows excellent storage capacity at high rates, attributed to the unique nanoneedle structure that high vacuum sputtering produces on the three-dimensional array. Following silicon’s success, titanium dioxide has been explored as an alternative highrate electrode material by utilizing the dual storage mechanisms of Li+ insertion and pseudocapacitance. The TiO[subscript]2-coated VACNFs shows improved electrochemical activity that delivers near theoretical capacity at larger currents due to shorter Li[superscript]+ diffusion lengths and highly effective electron transport. A unique cell is formed with the Si-coated and TiO[subscript]2-coated electrodes place counter to one another, creating the hybrid of lithium ion battery-pseudocapacitor that demonstrated both high power and high energy densities. The hybrid cell operates like a battery at lower current rates, achieving larger discharge capacity, while retaining one-third of that capacity as the current is raised by 100-fold. This showcases the VACNF arrays as a solid platform capable of assisting lithium active compounds to achieve high capacity at very high rates, comparable to modern supercapacitors. Lastly, manganese oxide is explored to demonstrate the high power rate performance that the VACNF array can provide by creating a supercapacitor that is highly effective in cycling at various high current rates, maintaining high-capacity and good cycling performance for thousands of cycles.

Master of Science / Mechanical and Nuclear Engineering / Kevin B. Lease / Gurpreet Singh / Energy has always been one of the most important factors in any type of human or industrial endeavor. Clean energy and alternative energy sources are slowly but steadily replacing fossil fuels, the over-dependence on which have led to many environmental and economic troubles over the past century. The main challenge that needs to be addressed in switching to clean energy is storing it for use in the electrical grid and transportation systems. Lithium ion batteries are currently one of the most promising energy storage devices and tremendous amount of research is being done in high capacity anode and cathode materials, and better electrolytes and battery packs as well, leading to overall high efficiency and capacity energy storage systems. Polymer derived ceramics (PDCs) are a special class of ceramics, usually used in high temperature applications, but some silicon based PDCs have demonstrated good electrochemical properties in lithium ion batteries. The goal of this research is to explore a special hybrid ceramic of titanium dioxide (TiO₂) and silicon oxy carbide (SiOC) ceramic derived from 1,3,5,7 -- tetravinyl -- 1,3,5,7 -- tetramethylcyclotetrasiloxane (TTCS) polymer for use in lithium ion batteries and investigate the source of its properties which might make the ceramic particularly useful in some highly specialized energy storage applications.