Rest Time Effect on the Series Resistance of Sodium-Metal Halide Battery

Sodium-Metal Halide Batteries are an interesting alternative to the Lithium-ion ones in stationary applications. However, their complex chemistry requires an accurate battery model to fully exploit the battery capabilities. The electric-equivalent models seem the best choice to predict the battery behavior, but state-of-the-art models still lack accuracy. This work shows the results of an experimental test campaign, in which significant variations of the battery series resistance have been observed during the relaxation time after a load application. This new phenomenon is not taken into account by the state-of-the-art model. However the results obtained show a resistance variation that reaches 17% of the resistance value at the beginning of the rest phase. A double-exponential function fits rather well the resistance variations as a function of the relaxation time obtaining a
$R^{2}$
coefficient of about 0.99.