context: To gain more insight into the morphological changes on the electrodes, as well as the causes of mNMR < mechem, we performed spectral fittings to determine how the relative fractions of the peaks assigned to Li microstructures vs. “bulk metal” change upon plating. The spectra were deconvoluted by using two peaks around 245–252.5 ppm (“bulk metal”) and one peak at around 257.5–262.5 ppm corresponding to the microstructural peak (see an example in Fig. 2f and more detailed explanation in the ESI†). We note that previous work has shown both experimentally and with simulations that dendrites and structures growing away from the Li metal surface give rise to larger shift around 270 ppm compared to microstructures close to the surface. In the current study, the in situ PEEK capsule cell applies constant pressure within the cell and more compact structures form, leading to a narrower range of shifts. The observed shifts of the microstructure peaks (Fig. S1†) are thus similar for both electrolytes although the microstructures have very distinct morphologies as seen in the SEM figures (Fig. 2b).