Studies of potential anode materials for lithium-ion batteries
Wood, Sean Michael
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Lithium-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.