Interpretation of 7 Li NMR Relaxation in Li 2 OHBr: Background Effects on Lorentzian Fits in Log Space

Solid-state NMR is increasingly used to study Li+ ion dynamics in crystalline and amorphous electrolytes designed as electronically insulating components in electrochemical energy storage systems. Recently, Milan et al. (ACS Mater. Lett. 2025, 7, 1187) reported diffusion-controlled 7Li NMR relaxation rates of Li2OHBr and analyzed them using BPP-type spectral density functions. However, their fitting procedure and results are difficult to follow and reproduce, especially regarding the treatment of BPP-type Lorentzian fits and background contributions in semilogarithmic representations. In this work, we reanalyze their rates while including an appropriate background contribution. For the X-ray amorphous, glassy Li2OHBr sample, two nearly ideal BPP processes are sufficient to describe the entire experimental response. Our extracted activation energies differ from those of Milan et al. and may alter the interpretation of their findings. Specifically, both the glassy and crystalline samples yield activation energies of 0.49 eV, independent of morphology. These values are in excellent agreement with recent (bulk) conductivity measurements and earlier NMR studies on Li2OHCl. The Arrhenius prefactors, reflecting attempt frequencies (3.8 × 1013 s–1 (glassy) and 1.8 × 1013 s–1 (crystalline)), vary only slightly but follow trends consistent with the observed 13 K shift of the main relaxation peaks. Notably, the slower motional process evident in the glassy sample is almost absent in the crystalline material.