UC Santa Barbara

The high energy density of lithium batteries is ideal for electric vehicles and spacecraft, which operate in extreme temperature environments. While the performance of lithium-ion and lithium metal batteries has been studied at moderate and elevated temperatures, the impact of low temperatures on lithium batteries is not well understood. This dissertation clarifies the effects of moderately low to cryogenic temperatures on lithium metal anodes, lithium-ion cathodes, and lithium organic electrolytes.We first consider the impact of moderately low temperature environments on lithium metal anodes. Using magnetic resonance imaging, we investigate lithium dendrite formation in a series of organic lithium electrolytes. We demonstrate that modification of a commercial lithium carbonate electrolyte with the addition of a diglyme cosolvent improves the low temperature performance of lithium metal anodes. This hybrid electrolyte reduces the evolution of unfavorable lithium microstructures through improved ionic transport properties and a modified SEI.We next consider the effect of ultralow temperature exposure on lithium-ion full cells. Relevant state-of-the-art lithium-ion batteries often consist of a nickel manganese cobalt oxide (NMC) cathode, a graphite anode, and an organic electrolyte. Cells with this chemistry are currently exposed to cryogenic temperatures in space; however, the impact of such extreme conditions is poorly understood. Freezing processes may cause physical degradation and cracking within electrodes and may disrupt the cation solvation structure. We consider the impact of exposing high-nickel NMC cathodes to cryogenic temperatures during cell rest. We observe that in NMC811|graphite coin cells, a cryogenic rest period has negligible impact on the NMC811 cathode structure, the chemistry of the cathode electrolyte interphase (CEI), and the cell performance. Finally, we investigate the fundamental phase behavior of a binary carbonate electrolyte system during freezing. Using magnetic resonance, diffraction, and spectroscopic techniques, we track long range and local structural evolution of eutectic and non-eutectic electrolytes from room temperature to cryogenic temperatures, demonstrating that the electrolytes undergo both freezing and vitrification while the lithium cation remains solvated.The following dissertation clarifies the effects of low temperatures on certain highly relevant lithium battery materials, which will contribute to more reliable technologies for use in extreme environments.