Angarita Gomez, Maria Stefany (2022-06). Dynamics and Mechanisms of Ion Transport Through Liquid and Amorphous Phases of Lithium Metal Batteries. Doctoral Dissertation.
Thesis
Lithium metal anode remains until this day as one promising alternative for better batteries as we move away from being fully reliant on fossil fuels and toward a more sustainable society. Lithium metal anode has a high theoretical capacity and low electrochemical potential. However, there are key factors related to the Lithium metal anode that have prevented the practical implementation of the lithium metal battery, in everyday devices. For instance, Lithium's extreme reactivity leads to the uncontrollable formation of solid electrolyte interphase (SEI) due to the electrolyte decomposition. Additionally, the uneven deposition of Lithium and formation of dendrites has hindered progress in the commercial use of this battery due to the loss of capacity that affects the performance during cycling, and induces safety issues. Several strategies involving both anode and electrolyte design have been implemented to improve battery performance. However, key questions remain in order to address the deposition of unwanted morphologies: what are the mechanisms that allow the ion transport through the liquid and solid interphases? And how do different environments affect this transport? And how is Li ion transport correlated to Li deposition morphology? Comprehensive answers to these questions will allow for the development of effective strategies that will facilitate the practical use of Lithium metal batteries. In this work, density functional theory (DFT), ab initio molecular dynamics (AIMD), and Thermodynamic Integrations resulting from constrained ab initio molecular dynamics (c-AIMD) simulations have been used to understand the mechanisms and dynamics of the ion transport through the liquid phase, at interfaces, and through the SEI interphases. These analyses provide fundamental insights that allow an improved interpretation of observed degradation modes. The effect of the electrolyte including solvent polarity and electron affinity, salt concentration, and presence of diluent was studied to understand the combined effect of each of these factors on the ion mobility through the electrolyte phase as well as at interfaces and interphases. Complementary to this work was the study of the SEI nucleation mechanism in small nanoclusters and the passivation effect of nanometer-thick layers to understand the structure and electron transferability of specific blocks. Finally, the transport of Li ions through SEI amorphous phases and associated energetic barriers provided additional fundamental understanding of ion diffusion and deposition and reduction pathway.
