Combining NMR and impedance spectroscopy in situ to study the dynamics of solid ion conductors

Abstract

Differences in activation energies of solid ion conductors as measured by different techniques can be either considered a consequence of experimental uncertainty or a valuable source of information about the local ion transport mechanism. Here, it is suggested that an in situ combination of solid-state nuclear magnetic resonance (NMR) and electrochemical impedance spectroscopy (EIS) helps to differentiate these two cases because the sample preparation and thermal history are then identical for the NMR and EIS measurement. To this end, an in situ NMR–EIS probe head is developed, calibrated and its performance is tested on the lithium-ion conductor Li₈SnO₆. For validation, the results were compared to carefully conducted ex situ measurements. The differences in activation energies as observed by NMR and EIS experiments could in this case be confirmed and rationalized by comparison to results from nudged elastic band calculation using density functional theory under periodic boundary conditions.