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

Na-23 MAS NMR spectra of sodium-oxygen (Na-O-2) 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 Na-23 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.