Tracking the Function and Failure of Li-Air Electrolytes using Electrochemical and Spectroscopic Methods

Li-air batteries (LABs) have gained significant attention due to their high gravimetric energy densities that are comparable to fossil fuels, with the added advantage of being greener than Lithium ion batteries, as they contain no transition metals. LABs rely on the reaction with O2 and the formation of a solid discharge product, usually Li2O2, which is then oxidised on charge. The main challenges associated with Li-air batteries include their high overpotentials, parasitic side reactions and dendritic growth at the Li-metal anode and degradation of the electrolyte. One way to overcome the high overpotentials is through the introduction of a redox mediator (RM), a soluble catalyst that facilitates the solution-based growth of discharge product and thereby extends the battery life. The kinetics of the electron transfer reaction of the RM with the target species (O2 on discharge and Li2O2 on charge) are directly related to the overpotential. These kinetics are often thought to be very fast but in reality they are often quasireversible and can limit the viable current density. The first chapter of the body of this thesis addresses this issue through a theoretical framework that can be utilised to analyse the thermodynamic and kinetic parameters of 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) as a RM in different Li-air electrolytes. Using Cyclic Voltammetry (CVs) and Electrochemical impedance Spectroscopy (EIS) the effect of ionic association is studied. The second chapter utilises 1H and 17O Nuclear Magnetic Resonance Spectroscopy (NMR) for the in situ monitoring of LAB electrolytes and to study their mechanisms and degradation. The third chapter addresses the issues associated with the Li-metal anode stability. The structure and growth of Li-microstructure is studied using in situ NMR as well as galvanostatic cycling and EIS. The effect of varying current densities and an Ar vs. O2 atmosphere is discussed.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Kunz, Vera

Advisor dc:contributor.advisor

• Grey, Clare

• Batteries
• Li-Air
• NMR

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/a4397d83-ae02-4d72-a421-f99cfeab30f2/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.115820

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/379849