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.

No abstract

No abstract

No abstract

In this work, we report on the research results of electrical impedance spectroscopy using a surface printed electrode with superficial modification using graphite nanoparticles and polymethyl-metaacrylate in three concentrations. The experiments used saline solutions of NaCl and KCl with a molar range between 0.287 to 3 M. Three parameters with nonlinear behaviour were used to adjust the molar concentration (MC); the correlation coefficients show a higher relationship (r2  >  0.9). This behavior depends on frequency, graphite and MC. The proposed electrode was found to have lower sensitivity to lower levels of NaCl or KCl which, in turn, might be a good electrical characteristic in order to detect a higher concentration in a solution. The modified electrode has advantages such as low cost, easy construction and lower saturation surface; future application of this sensor could be an industrial process or corrosion with brine water.