Insights Into Na-Ion Battery Conductivity from Mossbauer Spectroscopy

The motion of active ions in a battery is critical to all major issues facing electrochemical battery systems. A battery’s energy density, operating potential, and charge/discharge rate are determined by the ionic conductivity in the cathode. This work uses Mossbauer spectroscopy to assess the activation energy and electron dynamics in sodium-based Prussian blue analogs. The onset of polaron motion in each material is assessed through Mossbauer measurements at increasing temperatures and indicated by spectral distortions that occur when Na atoms become mobile and the iron atoms experience a fluctuating local environment. The critical role of Mossbauer spectroscopy in completing our understanding of conductivity in battery materials will be discussed alongside results for a series of sodium-iron Prussian blue analogs.