Browsing by Subject "Lithium-ion batteries"
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Item Development of nanostructured alloy-based composite anode materials for lithium- and sodium-ion batteries(2016-08) Kim, Sang Ok; Manthiram, Arumugam; Goodenough, John; Ferreira, Paulo; Yu, Guihua; Hwang, GyeongLithium-ion batteries are the dominant energy storage technology in portable electronic applications due to their high energy density, long cycle life, and low self-discharge rate. Efforts to extend their implementation into rapidly growing electric vehicles and large-scale stationary energy storage devices require further improvements of performance and safety, as well as cost reduction. In this regard, the development of low-cost, advanced electrode materials for next generation lithium-ion batteries or sodium-ion batteries is increasingly being pursued to achieve these requirements. The purpose of this dissertation is to explore and develop several types of composite alloy-based anodes that can possibly lead to the enhancement of lithium- or sodium-storage performance. Alloy anodes have shown great potential for realization of high-performance lithium- or sodium-ion battery systems with enhanced safety as they offer high theoretical specific capacity and higher operating voltages than graphite. In addition, the successful employment of earth-abundant materials such as silicon and phosphorus could also result in a reduction in battery manufacturing cost. However, the major obstacles associated with the large volume change upon electrochemical reactions give rise to severe capacity fading in the first few cycles, making their implementation into commercial cells quite challenging. In order to overcome this issue, the alloy-based composite anodes are synthesized by applying the active/inactive matrix concept. The composites are capable of possessing the following advantages: (i) structural reinforcement and suppression of particle agglomeration upon cycling through a mechanically durable buffer; (ii) enhanced electrochemical reversibility and fast electrode kinetics through nanoscale active materials; (iii) high conductivity and facile electron transport through a conducting phase; (iv) high chemical and electrochemical stability through an electrochemically inert buffer. Moreover, the composites synthesized have reasonably high tap density that is beneficial for improving the volumetric capacity of lithium- or sodium-ion cells. In this dissertation, three different low-cost alloy-based composite anodes are developed by a low-cost, facile, and scalable high-energy mechanical milling: silicon-, zinc-, and phosphorus-based composites. All the composite systems studied in this work demonstrate enhancements in lithium- or sodium-ion storage performance in terms of high capacity, long cycle life, and high rate capability, while maintaining high tap density. By controlling the type and amount of an inactive matrix, the effects of each inactive matrix on the electrochemical performance of the composite anodes are investigated. In addition, the mechanism for the performance improvement is discussed.Item A lithium conducting phase (Li₂Te) can obviate need for nanocrystallites in the lithiation/de-lithiation of Germanium(2015-08) Powell, Emily Janette; Mullins, C. B.; Heller, AdamMainstream rechargeable lithium battery materials research of the past 20 years has focused on nano-particulate materials, where Li⁺-diffusion lengths exceeded at designated cycling rates the particle radii, and where the particles slipped rather than broke upon their expansion and shrinkage in lithiation/de-lithiation cycles. Here we show that in intrinsically rapidly Li⁺-transporting macrocrystalline germanium and even more so in a dispersion of non-cycling Li₂Te in macrocrystalline germanium it is unnecessary to use nanocrystalline materials and that Li₂Te increases the retained capacity at 1C rate after 500 cycles. Dispersions of 10-30 atom % of crystalline GeTe in 90-70 atom % crystalline Ge were synthesized by quenching from the melt followed by high energy ball milling to 1μm-5μm particle size. The particles, as well as similarly made and similarly sized pure Ge particles were incorporated in electrodes, which were galvanostatically lithiated/de-lithiated. In the initial cycle, GeTe is reduced to Li[subscript x]Ge alloys and Li₂Te. In 500 1C cycles of Li[subscript x]Ge de-lithiation/Ge lithiation the capacity of the pure Ge faded more rapidly than that of the Ge electrodes containing Li₂Te, which retained 94-96 % of their initial capacity after 500 cycles at 1C rate.Item Low-temperature synthesis and electrochemical properties of aliovalently-doped phosphates and spinel oxides(2014-05) Gutierrez, Arturo, 1978-; Manthiram, ArumugamLithium-ion batteries are being intensely pursued as energy storage devices because they provide higher energy and power densities compared to other battery systems such as lead-acid and nickel-metal hydride batteries. This dissertation (i) explores the use of a low-temperature microwave-assisted synthesis process to obtain aliovalently-doped lithium transition-metal phosphates and lower-valent vanadium oxide spinels, some of which are difficult to obtain by conventional high-temperature processes, and (ii) presents an investigation of the electrochemical properties of the aliovantly-doped phosphate cathodes and doped lithium manganese oxide and oxyfluoride spinel cathodes in lithium-ion batteries. Following the introduction and general experimental procedures, respectively, in Chapters 1 and 2, Chapter 3 first focuses on understanding of how the inductive effect and structural features in lithium transition-metal borate, silicate, and phosphate cathodes affect the M²⁺ʹ³⁺redox energies. It is found that the magnitude of the voltages delivered by the polyanion cathodes can be predicted based simply on the coordination of the transition-metal ion. Furthermore, the differences in the voltages delivered by the phosphates and pyrophosphates are explained by considering the resonance structures and their contribution to the covalency of the polyanion. Chapter 4 presents a low-temperature microwave-assisted solvothermal process to substitute 20 atom % V³⁺ for Mn²⁺ in LiMnPO₄. It is shown that the solubility of vanadium in LiMnPO₄ decreases upon heating the doped samples to ≥ 575 °C, demonstrating the importance of employing a low-temperature process to achieve aliovalent doping in LiMnPO₄. It is further demonstrated that by increasing the vanadium content in the material, the discharge capacity in the first cycle could be increased without any additional carbon coating. Subsequent X-ray absorption spectroscopy data reveal that the better performance is facilitated by enhanced Mn-O hybridization upon incorporating vanadium into the lattice. Chapter 5 explores the influence of various factors, such as the oxidation state of Mn, electronegativity of the dopant cation Mn+, and the dissociation energy of M-O bond, on the electrochemical properties of cation-doped oxide and oxyfluoride spinel cathodes. As an extension, Chapter 6 presents the effect of processing conditions on the surface concentration of the dopant cation Mn+. Chapter 7 presents an extension of the low-temperature microwave-assisted synthesis process to obtain AV₂O₄ (Mg, Fe, Mn, and Co) spinel oxides. The method is remarkably effective in reducing the synthesis time and energy use due to the efficiency of dielectric heating compared to conventional heating. The ability to access V³⁺ is facilitated by the relative positions of the energy levels of the cations in solution, which is lower than that in the solid, and the use of a strong reducing solvent like TEG. Finally, Chapter 8 provides a summary of the salient findings in this dissertation.Item Studies of potential anode materials for lithium-ion batteries(2016-08) Wood, Sean Michael; Mullins, C. B.; Heller, Adam (Professor of chemical engineering); Manthiram, Arumugam; Hwang, Gyeong S; Yu, GuihuaLithium-ion batteries (LIBs) are currently used in nearly all consumer electronics, including cellular phones, laptop computers, and wearable devices such as smart watches. In the future, these batteries will also be used in electric vehicles and to store excess energy on a grid scale from intermittent sources such as wind and solar. On the anode side of LIBs, graphite has been the state-of-the-art material for the last 25 years and is reaching its technological limits, so research into new anode materials is needed in order to meet the increasing consumer demands for smaller, longer lasting batteries. The use of lead would be an incremental improvement over graphite since it has a higher capacity and is also cheap and abundant. A series of lead chalcogenides (PbO, PbS, PbSe, and PbTe) was synthesized, and their electrochemical properties were tested to determine their usefulness as potential LIB anode materials. PbO and PbS were found to perform poorly. PbSe performed better, although exhibited side reactions that rendered it unusable in actual LIBs. PbTe performed extremely well over the given testing window, able to be charged and discharged in only 30 minutes without suffering capacity fade. However, this material would be too expensive to use on a large scale due to tellurium’s rarity. Additionally, the 30 year old lithium-lead reaction mechanism in the literature was updated using a series of ex situ X-ray diffraction experiments. A step change improvement over graphite could come from using lithium metal, which would increase the anode capacity by a factor of 10. However, lithium metal suffers from uncontrollable dendritic growths which pose extreme safety hazards. An electrolyte additive was developed using potassium ions to overcome this dendrite issue. Dendritic growth was completely halted when this additive was used, and the cells cycled stably over the entire 18 day test period. The corrosion layer that forms on the surface of the lithium metal was characterized (via electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and time of flight – secondary ion mass spectrometry) and found to be altered by the presence of potassium, leading to the improved performance.Item The role of surface reactions and solid electrolyte interphase in silicon electrodes for lithium-ion batteries(2015-05) Schroder, Kjell William; Stevenson, Keith J.; Webb, Lauren J.; Korgel, Brian A; Milliron, Delia J; Henkelman, Graeme; Goodenough, John BIn order to utilize renewable energy sources to avoid adverse climate change caused by fossil fuel use, economical, efficient, and long-cycling energy storage means are needed for grid power applications and electric vehicles. Lithium-ion batteries (LIBs) are promising electrochemical energy storage devices for these applications, but capacity, cycle life, and device energy density need to be improved to meet these challenges. Silicon, as a lithium alloy, promises high gravimetric and volumetric charge capacities as a negative electrode in the next generation of LIBs. However silicon has a lithiation potential outside the window of stability of common non-aqueous liquid electrolytes (e.g., lithium hexafluorophosphate in ethylene carbonate and diethyl carbonate mixtures). Consequently, parasitic side reactions occur during continued lithiation and delithiation (cycling) of silicon. However, these side reactions (including electro-reduction and thermal decomposition) form insoluble products that make a solid electrolyte interphase (SEI), passivating an electrode’s surface. Cycling silicon electrodes can entail incomplete passivation (via unstable SEI species) and newly exposed surfaces (due to mechanical wear) and thus continued side reactions that lead to thermal runaway, capacity loss, and cell failure. By understanding interfacial electrode chemistry, it is hoped that novel design suggestions for addressing these problems will be uncovered. Model silicon electrodes studied by X-ray Photoelectron Spectroscopy (XPS), and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) were used to explore the effects of surface layer conductivity and electrolyte additives on SEI composition and structure. Anhydrous and anoxic techniques showed better reproducibility and accuracy in characterizing the SEI over previous studies of composite electrodes exposed to ambient conditions. By comparing silicon oxide and etched silicon surfaces, electrode conductivity was studied as well as how the co-solvent additive fluoroethylene carbonate (FEC) affects the SEI. Both the etched silicon surface and FEC produced SEI species like lithium fluoride that improved stability by resisting further electro-reduction. However, questions about the oxidative stability of some SEI species were raised (namely lithium oxide), suggesting a more stable artificial SEI could be manufactured compared to those formed during naive device operation.Item Understanding the electrochemical properties and safety characteristics of spinel cathodes for lithium-ion batteries(2013-05) Chemelewski, Katharine Rose; Manthiram, ArumugamManganese spinel cathodes LiMn₂O₄ offer the advantage of a strong, edge-shared octahedral framework with fast, 3-dimensional Li⁺-ion conduction. To better understand the safety of these materials, the thermal stability characteristics of spinel oxide and oxyfluoride cathodes Li[subscript 1.1]Mn[subscript 1.9-y]M[subscript y]O₄[subscript-z]F[subscript z] (M = Ni and Al, 0 ≤ y ≤ 0.3, and 0 ≤ z ≤ 0.2) have been investigated systematically. The thermal characteristics are assessed in terms of the onset temperature and reaction enthalpy for the exothermic reaction. The thermal stability increases with decreasing lithium content in the cathode in the charged state. High-voltage spinel cathodes LiMn[subscript 1.5]Ni[subscript 0.5]O₄ are promising candidates for electric vehicles and stationary storage of electricity produced by renewable energies due to their high power capability. However, widespread adoption of this high-voltage spinel cathode is hampered by severe capacity fade resulting from aggressive reaction with the electrolyte to form a thick solid-electrolyte interphase (SEI) layer. The synthesis conditions of the co-precipitation method are found to influence the microstructure and morphology through nucleation and growth of crystals in solution. Two samples prepared by similar wet-chemical routes have been characterized by microscopy and electrochemical methods to determine the role of microstructure and morphology on the electrochemical performance. It is found that the surface crystal planes play a key role in the capacity retention and rate performance. In order to achieve consistent electrochemical properties essential for the commercialization of the high-voltage spinel cathode LiMn[subscript1.5]Ni[subscript 0.5]O₄, the relationship between cation ordering, presence of impurity phase, and particle morphology must be elucidated. Accordingly, comparison of the stoichiometric LiMn[subscript1.5]Ni[subscript 0.5]O₄ cathodes with a Mn/Ni ratio of 3.0 prepared by different methods having varying morphologies and degrees of cation ordering is presented. It is found that although an increase in the degree of cation ordering decreases the rate capability, the crystallographic planes in contact with the electrolyte have a dominant effect on the electrochemical properties. To examine the effect of cation substitution on morphology, an investigation of the nucleation and growth of doped co-precipitated mixed-metal hydroxide precursor particles and the resulting stabilization of preferred crystallographic surface planes in the final spinel samples are presented. It is found that doping with certain cations stabilizes the growth of low-energy (111) surface planes, facilitating a long cycle life and fast high-rate performance. With an aim to develop a better understanding of the factors influencing the electrochemical properties, a systematic investigation of LiMn[subscript 1.5]Ni[subscript0.5-x]M[subscript x]O₄ (M = Cu and Zn and x = 0.08 and 0.16), in which Ni²⁺ ions are substituted by divalent Cu2+ and Zn2+ ions, is presented. It is found that although both Zn and Cu are divalent with ionic radii similar to that of Ni2+, they behave quite differently with respect to cation ordering and site occupancy, and higher levels of doping leads to distinct differences in cycling and rate performances.