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

Abstract

The reversible electrochemical process (insertion/extraction) of lithium ions in graphitic carbon was monitored in situ for the first time by 7Li nuclear magnetic resonance (NMR) spectroscopy using a novel NMR apparatus. The 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 graphitic 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 ~50 ppm is consistent with the interplane sites for lithium ions on the sixfold axis between two stacked aromatic carbon rings aligned in registry. The second predominant lithium signal at ~12 ppm occurs in the chemical shift region reported for high-stage lithiated graphite and a dispersion of lithium-ion sites found in disordered carbon matrices. In addition, we observed chemical shift signatures similar to those assigned to Li-7 nuclei in lithium oxide, lithium carbonate, lithium alkyls, and lithium alkoxides that occur near 0 ppm and represent lithium nuclei that are irreversibly bound in the electrode/electrolyte interphase. An increase in intensity in the spectral region that is normally associated with irreversibly bound lithium was observed during the first discharge cycle, as anticipated. However, the same peaks in the spectrum unexpectedly diminished during the subsequent charge cycle, suggesting that the interphase between the carbon electrode and the electrolyte is built up over several cycles.

Probing Operating Electrochemical Interfaces by Photons and Neutrons

“…During the last decade, a number of in situ NMR studies of electrochemical processes have been reported, although mainly bulk substances have been analysed. Since the present survey focuses on studies of electrochemical interfaces, the advantages of the NMR technique regarding studies of interfaces will be highlighted.…”

Carbon substitution for oxygen in silicates in planetary interiors

“…The isotropic chemical shift of the 6 Li resonance (−0.85 to −0.95 ppm) indicates that the majority of the Li + ions are in sixfold coordination with oxygen (21). The chemical shift range spanned by the 6 Li MAS NMR spectrum also suggests that Li-C bonding in the PDC would be unlikely because such resonances are expected to be shifted significantly to higher frequencies (22).…”

Automatic Tuning Matching Cycler (ATMC) in situ NMR spectroscopy as a novel approach for real-time investigations of Li- and Na-ion batteries

“…In situ nuclear magnetic resonance (NMR) spectroscopy was recently shown to be a valuable tool for these real-time studies of battery materials under operating conditions [6,[9][10][11][12][13][14][15][16]. Since the first in situ experiments approximately 15 years ago, two approaches regarding the NMR probe and/or the cell design have been established [11,17]: Toroid probeheads [18][19][20] and the use of commercial static NMR probes in which either Bellcore-type bag cells [21][22][23][24][25][26][27] or Swagelok-type plastic insets [28] were used. The toroid is both part of the electrochemical cell and NMR detector and was designed as a "battery imager" probe in its final set-up [18][19][20].…”

“…Since the first in situ experiments approximately 15 years ago, two approaches regarding the NMR probe and/or the cell design have been established [11,17]: Toroid probeheads [18][19][20] and the use of commercial static NMR probes in which either Bellcore-type bag cells [21][22][23][24][25][26][27] or Swagelok-type plastic insets [28] were used. The toroid is both part of the electrochemical cell and NMR detector and was designed as a "battery imager" probe in its final set-up [18][19][20]. A drawback of this design is an inherently low signal to noise (S/N) and complicated analysis of the spectra due to non-linear radio frequency (RF) excitation/detection.…”