1. Multinuclear NMR Probehead for in situ
Measurements in Lithium Ion Batteries
Prashant Mane, Umesh Katamkar, Vikas Kumar, C.V. Avadhani,
P.R. Rajamohanan, S. Ganapathy and S. Sivaram*
CSIR-National Chemical Laboratory, Pune
Introduction
NMR Probe Circuit
Li-ion Cell Developed
(13mm and 10 mm)
The radio frequency NMR probe circuit requires tuning of the frequency to the desired Larmor frequency (f0) and matching the impedance of the circuit to 50 ohms for optimum transfer of r.f power from the transmitter to the NMR coil. This is achieved with the tuning capacitor (C1) and matching capacitor (C2) in the series tapped (A) and parallel tapped (B) configurations of the basic resonance circuit as above.
Li-ion batteries are extensively used in both home devices (cell phones, laptops and cameras) as well as in commercial vehicles. Much of the battery performance in terms of charging, discharging and energy storage are intricately related to the choice of the actual materials used as electrodes, electrolytes and the separator. In order to understand the mechanistic events at the molecular level and to derive atomic insights during the actual electrochemical process, in situ measurements using the invaluable technique of NMR spectroscopy is very desirable. In an effort to move in this direction, we have designed and developed a Li-ion battery cell for carrying out in situ NMR experimental measurements. The salient features of the cell we have developed are highlighted. The cell also facilitates independent electrochemical conductivity experiments to be carried out. The performance of the cell has been examined both in conductivity studies as well as in NMR studies using 7Li and 31P nuclei.
13 mm NMR Teflon cell and its components
Graphite electrode
Stainless steel electrode
Separator (Celgard-2400)
A. Series Tapped (1H/19F)
B. Parallel Tapped (7Li, 31P)
For 1H /19F : C1 and C2: Johanson (5 to 25 pF)
For 7Li /31P : C1 and C2: Polyflon (0.8 to 18 pF)
Design Considerations
The Li ion battery cell design is chosen such that the cell can be adapted for independent in situ NMR as well as in situ conductivity measurements. NMR experimental measurements were carried out using Bruker 400 MHz NMR spectrometer at NCL, Pune and at University of Madras, Chennai.
A larger volume cell (13 mm diameter), in addition to the conventional 10 mm diameter cell, was employed for NMR measurements of nuclei with low detection sensitivity (13C, 6Li).
NMR probe design is such that it allows radio frequency tunability over a large frequency range on the broad band F2 channel and 1H and 19F on the F1 channel to facilitate both homonuclear and heteronuclear 1D and 2D experiments
NMR Probehead Developed
NMR Performance of the Probe with the Cell
Impedance measurements of Li-ion Teflon Cell of 13 mm and 10 mm Diameter in Actual Battery Conditions
7Li-NMR spectra of LiCl in glass tube in fabricated NMR probehead
31P-NMR spectra of H3PO4 in glass tube in fabricated NMR probehead
7Li-NMR spectra of LiCl in fabricated Teflon NMR cell in fabricated NMR probehead under battery condition
31P-NMR spectra of H3PO4 in fabricated Teflon NMR cell in fabricated NMR probehead under battery condition
Impedance measurement in 13 mm Teflon NMR cell
Impedance measurement in 10 mm Teflon NMR cell
Impedance graph of Polyetherimide
Impedance graph of Celgard-2400
References
Summary and Conclusion
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4. “Practical Exercises for Learning to Construct NMR/MRI Probe Circuits”
D.D. Wheeler and M.S. Conradi, Concepts in Magnetic Resonance 2012, 40A,1-13.
Li-ion cell for conductivity measurements and NMR Spectral measurements has
been developed.
The cells of 13 mm and 10 mm diameter have been adapted in a home-built
NMR Probehead which is also mean design and constructed.
Present configuration allowed in situ conductivity experiments to be performed using 13 mm
and 10 mm cells, besides enabling ex situ 7Li and 31P NMR experiments to be
carried out using a large volume in 13 mm Li-ion cell.
Further efforts are under way to add full multinuclear capability in a double
resonance (X- 1H/19F) confirmation.
Acknowledgement
Vikas Kumar Acknowledges CSIR for funding