Martin Süfke

 

Low Field Nuclear Magnetic Resonance on Lithium Ion Batteries

Low Field NMR Setup at RWTH Aachen, working group of Prof. S. Appelt.  left: 180mm bore low field electromagnet, right: low field NMR probe head. Copyright: M. Süfke

Nuclear Magnetic Resonance (NMR) is in widespread use as a spectroscopic as well as an imaging method in applications from physics, chemistry, biology and engineering sciences. Under the name Magnetic Resonance Imaging (MRI) it is a standard imaging method for medical applications and material sciences.

However, traditional NMR or MRI setups require very strong magnetic fields (10-24 T) which mandate the use of superconducting magnets at liquid Helium temperatures (4 K). The associated cryogenic equipment restricts access to the sensitive volume and makes the whole equipment expensive to operate.

In the last decade, a number of smaller NMR spectrometer and imaging devices has emerged, operating at vastly lower magnetic fields at or below 1 Tesla. A very special low field (LF-) NMR spectrometer, operating at 0.05-20 mT has been conceived, built and developed by Prof. Stephan Appelt [1-5]. This design features a very large bore (180 mm), enabling the analysis of large samples and an electromagnet with an ultra-stable current supply. The large volume of homogeneous field (1x1x1 cm³) and the very good temporal stability (dB/dt < 1 ppm/min) allow the recording of highest resolution spectra of many different Nuclei (1H, 6Li , 19F, 31P , 129Xe ) [2-4].

Conventional NMR (400 MHz – 1000 MHz) suffers from eddy currents and skin-effect problems when it comes to detecting inner details of Lithium batteries [6]. LF-NMR is expected to be less sensitive to these kinds of problems because at low magnetic fields (at small frequencies 20 – 500 kHz) the skin depth is larger and the radio frequency can penetrate the conductive components. Therefore, LF-NMR could be a promising method to analyze Lithium ion battery components, specially the electrolyte and SEI interface layer. This work is aimed at making this possible by enabling the existing LF-NMR setup at RWTH Aachen to work with components and representative models of Lithium batteries.

References:

[1] Text mit Link: Webseite Prof . Stephan Appelt Link zum Text: http://www.mc.rwth-aachen.de/aw/cms/MC/Themen/Huelle_Personen/personen/Mitarbeiter/~vfm/appelt/?lang=en

[2] S. Appelt et. al. “Chemical analysis by ultrahigh-resolution nuclear magnetic resonance in the Earth's magnetic field”. Nat. Phys. 2, 105 (2006).

[3] S. Appelt et. al. “Mobile High Resolution Xenon Nuclear Magnetic Resonance Spectroscopy in the Earth´s Magnetic Field”, Phys. Rev. Lett. 94, 197602 (2005).

[4] S. Appelt et. al. ; “Fundamental Aspects of Parahydrogen Enhanced Low-Field Nuclear Magnetic Resonance”, Phys. Rev. Lett. 230, 176-185 (2013)

[5] S. Appelt et. al. ; “Studies of 6Li-NMR properties in different salt solutions in low magnetic fields”, J. Magn. Reson. 214, 10-14 (2012)

[6] A. Jerschow et. al. “Visualizing skin effects in conductors with MRI: 7Li MRI experiments and calculations”, J. Magn. Reson. 245, 143–149 (2014)