"In Situ Imaging of Charge Carriers in an Electrochemical Cell"

R. E. Gerald I , R. J. Klingler, J. W. Rathke, G. Sandí, and K. Woelk, in "Spatially Resolved Magnetic Resonance", P. Blümler, B. Blümich, R. Botto, E. Fukushima (Eds.), 111-119, Wiley-VCH, Weinheim (1998).

• A toroid cavity nuclear magnetic resonance (NMR) detector capable of quantitatively recording radial concentration profiles, diffusion constants, displacements of charge carriers, and radial profiles of spin-lattice relaxation time constants was employed to investigate the charge/discharge cycle of a solid-state electrochemical cell.

• One-dimensional radial concentration profiles (1D-images) of ions solvated in a polyethylene oxide matrix were recorded by ¹⁹F and ⁷Li NMR for several cells. A sequence of ¹⁹F NMR images, recorded at different stages of cell polarization, revealed the evolution of a region of the polymer depleted of charge carriers. From these images it is possible to extract the transference number for the Li⁺ ion. Spatially localized diffusion coefficients and spin-lattice relaxation time constants can be measured simultaneously for the ions in the polymer electrolyte by a spin-labeling method that employs the radial B¹-field gradient of the toroid cavity. A spatial resolution of 7 µm near the working electrode was achieved with a gradient strength of 800 gauss/cm.

• With this apparatus, it is also possible to investigate novel intercalation anode materials for lithium ion storage. These materials are coated onto the working electrode in a thin film. The penetration depth of lithium cations in these films can be imaged at different times in the charge/discharge cycle of the battery.

K. Woelk, September 25, 2000