Molecular-Level Understanding of Electrochemical Reaction Mechanisms and Electrode Interphases in Metal-CFx Batteries

<p>The development of high-energy-density battery materials is crucial for applications spanning from electric vehicles to space exploration. Metal anode and conversion-type batteries provide higher specific energy compared to conventional intercalation-based systems. Among these, metal-carbon monofluoride (CF_x) batteries, such as lithium-CF_x (Li/CF_x), stand out due to their high specific energies and wide operating temperatures, making them suitable for diverse applications including implantable medical devices, marine, military, and aerospace missions. Notably, Li/CF_x batteries are lead candidates for space exploration and planetary science, such as the Europa lander mission concept, owing to their high gravimetric energy density (2180 Wh kg⁻¹) and low self-discharge rates. However, key scientific challenges remain that inhibit their technological development, including limited molecular-level understanding of the electrochemical reaction mechanisms, how the materials are affected by radiation, and how the discharge products and electrode films and interfaces evolve with age. In addition, the origin of large overpotentials and possibility of rechargeability remain areas of investigation.</p> <p>Herein, the electrochemical reaction mechanisms and chemical processes in Li/CF_x and fluoride-ion (F-ion) metal/CF_xbatteries were elucidated up from the molecular level via a combination of electrochemical experiments, solid-state nuclear magnetic resonance (NMR) spectroscopy, and other spectroscopic and surface science measurements. NMR spectroscopy, uniquely suited for probing environments, composition, dynamics, and interactions up from the atomic scale, was instrumental in understanding the molecular-scale evolution of moieties in the CF_x electrodes during discharge, aging, and under radiation.</p> <p>New insights into Li/CF_x batteries revealed that the electrochemically formed discharge product, LiF, disperses into the electrolyte as a colloidal suspension, a previously unrecognized phenomenon confirmed through dynamic light scattering as well as optical microscopy and supported by thermodynamic analyses of open-circuit potentials. Addressing this process enabled the development of a method to accurately monitor LiF growth and determine the battery’s depth-of-discharge via electrochemical impedance spectroscopy. Additionally, the impact of gamma-ray radiation on both the CF_x and lithium metal electrodes was studied, linking radiation-induced defects to the decomposition, and restructuring of the electrode films. While the CF_x electrode exhibited resistance to radiation effects, LiF proved susceptible to radiation-induced defects that altered its electronic structure. Furthermore, the electrochemical defluorination of CF_x electrodes at room temperature was demonstrated using a liquid fluoride-ion conducting electrolyte paired with various metal anodes. Solid-state NMR spectroscopy and X-Ray diffraction measurements elucidated a novel fluoride-ion discharge mechanism that reduced polarization loss and has potential to achieve higher practical discharge voltages than conventional Li/CF_x batteries. Overall, this work advances scientific understanding of Li/CF_x and emerging F-ion metal/CF_x battery chemistries. The integration of solid-state NMR and electrochemical experiments proved invaluable in elucidating electrochemical reaction mechanisms and establishing critical links between macroscopic properties and interfacial phenomena in battery materials.</p>

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical Engineering

Year dc:date.available

2025

Author dc:creator

• Robinson, Loleth E

Contributors dc:contributor

• Robert Messinger

• lithium batteries
• primary batteries
• interphases
• carbon monofluoride
• electrochemical impedance spectroscopy
• solid-state nuclear magnetic resonance
• Chemical Engineering
• Chemistry
• Materials Science and Engineering

Repository record dc:identifier

https://academicworks.cuny.edu/cc_etds_theses/1271

OAI identifier oai:identifier

oai:academicworks.cuny.edu:cc_etds_theses-2329