Detection of Electrochemical Reaction Products from the Sodium–Oxygen Cell with Solid-State 23Na NMR Spectroscopy

²³Na MAS NMR spectra of sodium-oxygen (Na-O₂) cathodes reveals a combination of degradation species: newly observed sodium fluoride (NaF) and the expected sodium carbonate (Na₂CO₃), as well as the desired reaction product sodium peroxide (Na₂O₂). The initial reaction product, sodium superoxide (NaO₂), is not present in a measurable quantity in the ²³Na NMR spectra of the cycled electrodes. The reactivity of solid NaO₂ is probed further, and NaF is found to be formed through a reaction between the electrochemically generated NaO₂ 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.