The Impact of Degradation Reactions on Aprotic Metal-O2 Battery Performance
The need for new portable energy storage technologies places increasing demand on the development of new batteries beyond Li-ion. Potential candidates to fill this necessity are the class of metal-O2 batteries. In particular, Li-O2 batteries offer a theoretical energy density of ~ 3,000 Wh/kg; a huge leap in energy storage beyond that of today’s traditional batteries. The energy is derived from the electrochemical reaction of Li+ with gaseous oxygen, O2, to form Li2O2, which is stored on the positive electrode surface. Current-day aprotic Li-O2 batteries cannot reach these high theoretical energy densities, however, because they are plagued with pitfalls, including poor capacity retention, low rate capabilities, and high voltage inefficiencies. This is a result of electrode and electrolyte degradation reactions that occur during normal cell operation. This thesis explores the source of these inefficiencies, and focuses on the electrode and electrolyte degradation reactions that arise during cell operation. To support this thesis, the following is presented: 1. Methods for screening the stability of electrolytes and electrode materials towards the highly nucleophilic O2-/Li2O2. 2. The impact of electrolyte instability and by-product formation has on the Li-O2 oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activity, along with a discussion of the validity of a Li2O2 OER catalyst. 3. The design, development, and construction of an on-line mass spectrometer for quantitative analysis of the metal-O2 chemistry. 4. The importance of quantifying the ORR/OER efficiency, demonstrated through the use of mass spectrometry, where understanding the actual metal-O2 chemistry is crucial to form proper conclusions. 5. A study on the stability of various cell components in the Na-O2 battery to contrast the viability of the Na-O2 battery as a potential candidate moving forward.