2 research outputs found
Detection of Electrochemical Reaction Products from the Sodium–Oxygen Cell with Solid-State <sup>23</sup>Na NMR Spectroscopy
<sup>23</sup>Na MAS NMR spectra of sodium–oxygen (Na–O<sub>2</sub>) cathodes reveals a combination of degradation species: newly
observed sodium fluoride (NaF) and the expected sodium carbonate (Na<sub>2</sub>CO<sub>3</sub>), as well as the desired reaction product sodium
peroxide (Na<sub>2</sub>O<sub>2</sub>). The initial reaction product,
sodium superoxide (NaO<sub>2</sub>), is not present in a measurable
quantity in the <sup>23</sup>Na NMR spectra of the cycled electrodes.
The reactivity of solid NaO<sub>2</sub> is probed further, and NaF
is found to be formed through a reaction between the electrochemically
generated NaO<sub>2</sub> and the electrode binder, polyvinylidene
fluoride (PVDF). The instability of cell components in the presence
of desired electrochemical reaction products is clearly problematic
and bears further investigation
How to Control the Discharge Products in Na–O<sub>2</sub> Cells: Direct Evidence toward the Role of Functional Groups at the Air Electrode Surface
Sodium–oxygen
batteries have received a significant amount
of research attention as a low-overpotential alternative to lithium–oxygen.
However, the critical factors governing the composition and morphology
of the discharge products in Na–O<sub>2</sub> cells are not
thoroughly understood. Here we show that oxygen containing functional
groups at the air electrode surface have a substantial role in the
electrochemical reaction mechanisms in Na–O<sub>2</sub> cells.
Our results show that the presence of functional groups at the air–electrode
surface conducts the growth mechanism of discharge products toward
a surface-mediated mechanism, forming a conformal film of products
at the electrode surface. In addition, oxygen reduction reaction at
hydrophilic surfaces more likely passes through a peroxide pathway,
which results in the formation of peroxide-based discharge products.
Moreover, in-line X-ray diffraction combined with solid state <sup>23</sup>Na NMR results indicate the instability of discharge products
against carbonaceous electrodes. The findings of this study help to
explain the inconsistency among various reports on composition and
morphology of the discharge products in Na–O<sub>2</sub> cells
and allow the precise control over the discharge products