Date of Award
Doctor of Philosophy (PhD)
Rechargeable alkali metal anodes hold the promise to significantly increase the energy density of current battery technologies. But they are plagued by dendritic growths and solid-electrolyte interphase (SEI) layers that undermine the battery safety and cycle life. The path towards high-performance alkali metal batteries requires multiscale understanding and optimization, from nanoscale solvation structure, microscale morphology and interphase chemistry, to macroscale metal-separator interaction. This dissertation focuses on the following aspects: (i) dynamic electrode|electrolyte interfacial stability optimization for stable anode-free alkali metal batteries, (ii) electrode|separator interfacial stability analysis of the stabilized metal anodes, (iii) Li plating in commercial Li-ion batteries at extreme conditions. In the first part, we report a non-porous ingot-type sodium metal growth with self-modulated shiny-smooth interfaces that can be cycled reversibly, without forming whiskers, mosses, gas bubbles, or disconnected metal particles that are usually observed in other studies. The ideal interfacial stability enables anode-free Na metal full cells with a superior capacity retention rate of 99.93% per cycle. Contradictory to the common beliefs established around alkali metal anodes, there is no repeated SEI formation on or within the sodium anode, supported by the X-ray photoelectron spectroscopy elemental depth profile analyses, electrochemical impedance spectroscopy diagnosis and microscopic imaging. A similar stability was also achieved for the K metal anode. Comparative investigations confirm the importance of interfacial solvation structures in achieving the ideal morphological stability and facile charge transfer kinetics. In the second part, we use the ideally stable ingot-type sodium metal anode as a model system to identify the fast-charging limits, i.e. highest safe current density, of metal anodes. Our results show that metal penetration can still occur at relatively low current densities, but the overpotentials at the penetration depend on the pore sizes of the separators and surprisingly follow a simple mathematical model we developed as the Young-Laplace overpotential. Our study suggests that the success of stable metal batteries with even the ideally smooth metal anode requires the holistic design of the electrolyte, separator, and metal anodes to ensure penetration-free operation. In the third part, we fabricate Li-ion full cells in transparent glass capillaries to probe the real-time dynamic evolution of the lithiated phases throughout the graphite anode toward the onset of lithium plating during fast charging and under low temperatures. We observed that Li plating can occur well before 70% state of charge (SOC), even at a low C-rate and at room temperature. Our operando experiments provide the direct proof that subtle features in the electrochemical responses are caused by the Li plating, which can be utilized to improve battery management strategy. Mathematical simulations confirm that the local overpotential due to the strong concentration polarization is the root cause of the axial reaction heterogeneity in the graphite anode and the Li plating on the fully lithiated particles.
Peng P. Bai
Pratim P. Biswas, Vijay V. Ramani, Zhen Z. He, Srikanth S. Singamaneni,
Available for download on Wednesday, May 15, 2024