Yoshiki Iwai

Lithium ion diffusion in Li β-alumina single crystals measured by pulsed field gradient NMR spectroscopy

The lithium ion diffusion coefficient of a 93% Li β-alumina single crystal was measured for the first time using pulsed field gradient (PFG) NMR spectroscopy with two different crystal orientations. The diffusion coefficient was found to be 1.2 × 10(-11) m(2)/s in the direction perpendicular to the c axis at room temperature. The Li ion diffusion coefficient along the c axis direction was found to be very small (6.4 × 10(-13) m(2)/s at 333 K), which suggests that the macroscopic diffusion of the Li ion in the β-alumina crystal is mainly two-dimensional. The diffusion coefficient for the same sample was also estimated using NMR line narrowing data and impedance measurements. The impedance data show reasonable agreement with PFG-NMR data, while the line narrowing measurements provided a lower value for the diffusion coefficient. Line narrowing measurements also provided a relatively low value for the activation energy and pre-exponential factor. The temperature dependent diffusion coefficient was obtained in the temperature range 297-333 K by PFG-NMR, from which the activation energy for diffusion of the Li ion was estimated. The activation energy obtained by PFG-NMR was smaller than that obtained by impedance measurements, which suggests that thermally activated defect formation energy exists for 93% Li β-alumina single crystals. The diffusion time dependence of the diffusion coefficient was observed for the Li ion in the 93% Li β-alumina single crystal by means of PFG-NMR experiments. Motion of Li ion in fractal dimension might be a possible explanation for the observed diffusion time dependence of the diffusion coefficient in the 93% Li β-alumina system.

Observation of Electrophoretic Nuclear Magnetic Resonance Imaging in Polymer Electrolyte

We studied proton dynamics in polymer electrolyte by nuclear magnetic resonance imaging (NMR imaging or MRI) combined with DC electric field. Two pulse sequences: Spin-Echo and RARE (rapid acquisition with relaxation enhancement techniques) methods are used to obtain the spin density distribution in the membrane and fine time resolution images. Migration process of water from anode to cathode was observed by NMR imaging while applying DC electric field. The diffusion coefficient evaluated from proton mobility measured by NMR imaging and self-diffusion coefficient measured by pulse-field gradient method has almost same order of magnitude. The intensity enhancement in the vicinity of Pt electrode was detected when DC polarity was inverted. It implies attracted protons (H + ) on Pt electrode react with dissolved oxygen gases to generate water.

Vibrational Analysis of Ion Dynamics in Ag β-Alumina by Raman and Molecular Dynamics Simulation

The Raman spectra of single crystal Ag β-alumina have been measured at room temperature. The interatomic potential was evaluated by a non-linear least square fitting between phonon eigenvalues from Raman and dynamical matrix calculation. Using the obtained pair-potentials, the MD simulation was performed. In order to understand the many-body effects for the fast ion conduction in super ionic conductor, the three kinds of Ag–Ag interaction energies were assumed. The potential barrier height for jump diffusion depends on the magnitude of the repulsive force between mobile ions. It gives a new insight into an ion dynamics of super ionic conductor.

Nuclear Magnetic Resonance Study of Lithium-Ion Batteries

In this chapter, the application of nuclear magnetic resonance (NMR) to lithium-ion batteries is discussed. It is shown that observation of lithium in anode carbon materials is straightforward and in situ NMR during charge/discharge has been realized. Examination of solid-state NMR of various nuclear spins in electrode materials using a technique called magic-angle spinning (MAS) is introduced. Further, measurement of the diffusion coefficient and observation of magnetic resonance imaging (MRI) of lithium-ion batteries using the pulsed-field-gradient technique are discussed.