Rate-Dependent Nucleation and Growth of NaO2 in Na-O-2 Batteries

TitleRate-Dependent Nucleation and Growth of NaO2 in Na-O-2 Batteries
Publication TypeJournal Article
Year of Publication2015
AuthorsOrtiz-Vitoriano, N, Batcho, TP, Kwabi, DG, Han, B, Pour, N, Yao, KPierre Cla, Thompson, CV, Shao-Horn, Y
JournalJournal of Physical Chemistry Letters
Pagination2636 - 2643
Date Published2015/07/02/

Understanding the oxygen reduction reaction kinetics in the presence of Na ions and the formation mechanism of discharge product(s) is key to enhancing Na-O-2 battery performance. Here we show NaO2 as the only discharge product from Na-O-2 cells with carbon nanotubes in 1,2-dimethoxyethane from X-ray diffraction and Raman spectroscopy. Sodium peroxide dihydrate was not detected in the discharged electrode with up to 6000 ppm of H2O added to the electrolyte, but it was detected with ambient air exposure. In addition, we show that the sizes and distributions of NaO2 can be highly dependent on the discharge rate, and we discuss the formation mechanisms responsible for this rate dependence. Micron-sized (similar to 500 nm) and nanometer-scale (similar to 50 nm) cubes were found on the top and bottom of a carbon nanotube (CNT) carpet electrode and along CNT sidewalls at 10 mA/g, while only micron-scale cubes (similar to 2 mu m) were found on the top and bottom of the CNT carpet at 1000 mA/g, respectively.