Date of Graduation
5-2025
Document Type
Thesis
Degree Name
Master of Science in Mechanical Engineering (MSME)
Degree Level
Graduate
Department
Mechanical Engineering
Advisor/Mentor
Meng, Xiangbo
Committee Member
Fritsch, Ingrid
Second Committee Member
Hu, Han
Keywords
In-Situ Optical Microscopy; Lithium Dendrites; Lithium Metal Anodes
Abstract
This thesis presents an in-situ optical microscopy technique for observing dendritic deposition of lithium ions onto lithium metal electrodes. Current research methods and findings using in-situ and operando optical microscopy are discussed. Future works relevant to lithium metal anode implementation are explored. This paper discusses the procedure for constructing an effective in-situ optical microscopy visualization cell and the difficulties that arise during construction. Lithium metal symmetrical cells were constructed with 1 M bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) in 1:1 by volume dioxolane/dimethoxyethane (DOL/DME) electrolyte (i.e., 1 M LiTFSI in 1:1 DOL/DME, referred to as the ether electrolyte) and with 1.2 M lithium hexafluorophosphate (LiPF6) in 3:7 by weight ethylene carbonate/ethyl methyl carbonate (EC/EMC) electrolyte (i.e., 1.2 M LiPF6 in 3:7 EC/EMC, referred to as the carbonate electrolyte). The dendrite morphology in these electrolytes was compared via in-situ optical microscopy (OM) imaging, in-situ electrochemical impedance spectroscopy (EIS), and ex-situ scanning electron microscopy (SEM). Comparative experiments are conducted with symmetrical lithium metal coin cells in the same electrolytes. In the ether electrolyte studies, in-situ OM reveals a nearly uniform distribution of dendrite nucleation sites across the lithium metal surface, with a constant increase in thickness throughout the plating half-cycle at various current densities. The lithium deposition in the carbonate electrolyte exhibited sporadic nucleation sites with large discrepancies in growth rate of each dendrite. Ex-situ SEM investigations of the working electrode in ether electrolyte studies revealed large, uniform filament size across the electrode. The working electrode in the carbonate electrolyte study showcased dendrites with a morphology resembling a bush, with individual filaments too small to analyze. These dendrites were also variable in size and easily broken or removed from the surface. EIS was utilized to examine the development of the native layer on the surface of the lithium metal before electrochemical cycling as well as to investigate the impedance across the cell after a plating half-cycle. All studies using the ether electrolyte exhibited lower impedance than the same experiments with the carbonate electrolyte. All of these results indicate that the ether electrolyte is more compatible with lithium metal and promotes a beneficial solid electrolyte interphase for electrochemical cycling.
Citation
Lindsey, I. (2025). In Situ Studies on Lithium Dendrite Growth Using Optical Microscopy. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5693
