Interfacial Effects on Lithium Superoxide Disproportionation
in Li-O<sub>2</sub> Batteries
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Abstract
During the cycling of Li-O<sub>2</sub> batteries the
discharge process gives rise to dynamically evolving agglomerates
composed of lithium–oxygen nanostructures; however, little
is known about their composition. In this paper, we present results
for a Li-O<sub>2</sub> battery based on an activated carbon cathode
that indicate interfacial effects can suppress disproportionation
of a LiO<sub>2</sub> component in the discharge product. High-intensity
X-ray diffraction and transmission electron microscopy measurements
are first used to show that there is a LiO<sub>2</sub> component along
with Li<sub>2</sub>O<sub>2</sub> in the discharge product. The stability
of the discharge product was then probed by investigating the dependence
of the charge potential and Raman intensity of the superoxide peak
with time. The results indicate that the LiO<sub>2</sub> component
can be stable for possibly up to days when an electrolyte is left
on the surface of the discharged cathode. Density functional calculations
on amorphous LiO<sub>2</sub> reveal that the disproportionation process
will be slower at an electrolyte/LiO<sub>2</sub> interface compared
to a vacuum/LiO<sub>2</sub> interface. The combined experimental and
theoretical results provide new insight into how interfacial effects
can stabilize LiO<sub>2</sub> and suggest that these interfacial effects
may play an important role in the charge and discharge chemistries
of a Li–O<sub>2</sub> battery
