In situ nuclear magnetic resonance investigations of lithium ions in carbon electrode materials using a novel detector

The reversible electrochemical process (insertion/extraction) of lithium io ns in graphitic carbon was monitored it? situ for the first time by Li-7 nu clear magnetic resonance (NMR) spectroscopy using a novel NMR apparatus. Th e compression coin cell battery imager is a simple device that combines the functions of an electrochemical cell and an NMR detector. A series of 7Li NMR spectra obtained for a blend of spherical and flaky disordered graphiti c carbon particles revealed two distinct chemical shift signatures for the lithium ions that were inserted and extracted in the first electrochemical cycle. The lithium signal at similar to 50 ppm is consistent with the inter plane sites for lithium ions on the sixfold axis between two stacked aromat ic carbon rings aligned in registry. The second predominant lithium signal at similar to 12 ppm occurs in the chemical shift region reported for high- stage lithiated graphite and a dispersion of lithium-ion sites found in dis ordered carbon matrices. In addition, we observed chemical shift signatures similar to those assigned to Li-7 nuclei in lithium oxide, lithium carbona te, lithium alkyls, and lithium alkoxides that occur near 0 ppm and represe nt lithium nuclei that are irreversibly bound in the electrode/electrolyte interphase. An increase in intensity in the spectral region that is normall y associated with irreversibly bound lithium was observed during the first discharge cycle, as anticipated. However, the same peaks in the spectrum un expectedly diminished during the subsequent charge cycle, suggesting that t he interphase between the carbon electrode and the electrolyte is built up over several cycles.