ABSTRACT
We studied the local structure and the Li ion dynamics in electrochemically and chemically prepared Li(4+x)Ti(5)O(12) with x = 0 5. We used magic-angle spinning (7)Li NMR on samples with different Li contents to investigate the sites that are occupied/emptied during Li insertion/removal. While the electrochemical measurements show a lithium insertion in two steps, 1D MAS NMR as a function of the lithium content shows that the overall spectral evolution observed during lithium insertion is inverted during lithium removal. Thereby the second insertion step is associated with an increased structural disorder. For samples with x = 0, 2, 3, and about 5, we performed temperature-dependent measurements of the (7)Li NMR relaxation rates T(1)(-1), T(2)(-1), and T(1ρ)(-1) to study the dynamics of the Li ions. For the samples with x = 0, 2, and 3, activation energies of (0.45 ± 0.1)eV were obtained. The highest mobility of the Li ions is observed for the samples with x = 2 and 3. Results from (6)Li and (7)Li 2D exchange MAS NMR spectroscopy on samples with x = 2 and 4 show that magnetization transfer for (7)Li below 323K is dominated by spin diffusion.
