Postmortem 7Li NMR analysis for assessing the reversibility of lithium metal electrodes in lithium metal batteries

Abstract

Despite the proficiency of lithium (Li)-7 NMR spectroscopy in delineating the physical and chemical states of Li metal electrodes, challenges in specimen preparation and interpretation impede its progress. In this study, we conducted a comprehensive postmortem analysis utilizing 7Li NMR, employing a standard magic angle spinning probe to examine protective-layer coated Li metal electrodes and LiAg alloy electrodes against bare Li metal electrodes within Li metal batteries (LMBs). Our investigation explores the effects of sample burrs, alignment with the magnetic field, the existence of liquid electrolytes, and precycling on the 7Li NMR signals. Through contrasting NMR spectra before and after cycling, we identified alterations in Li0 and Li+ signals attributable to the degradation of the Li metal electrode. Our NMR analyses decisively demonstrate the efficacy of the protective layer in mitigating dendrite and solid electrolyte interphase formation. Moreover, we noted that Li+ ions near the Li metal surface exhibit magnetic susceptibility anisotropy, revealing a novel approach to studying diamagnetic species on Li metal electrodes in LMBs. This study provides valuable insights and practical guidelines for characterizing distinct lithium states within LMBs.