The cubic spinel oxides Li(1+x)Ti(2-x)O(4) (0 < or =x< or = 1/3) are promising anode materials for lithium-ion rechargeable batteries. The end member of the Li-Ti-O series, Li(4)Ti(5)O(12), can accommodate Li ions up to the composition Li(7)Ti(5)O(12). Whereas a number of studies focus on the electrochemical behaviour of Li insertion into and Li diffusion in the Li intercalated material, only few investigations about low-temperature Li dynamics in the non-intercalated host material Li(4)Ti(5)O(12) have been reported so far. In the present paper, Li diffusion in pure-phase microcrystalline Li(4)Ti(5)O(12) with an average particle size in the microm range was probed by (7)Li solid state NMR spectroscopy using spin-alignment echo (SAE) and spin-lattice relaxation (SLR) measurements. Between T = 295 K and 400 K extremely slow Li jump rates tau(-1) ranging from 1 s(-1) to about 2200 s(-1) were directly measured by recording the decay of spin-alignment echoes as a function of mixing time and constant evolution time. The results point out the slow Li diffusion in non-intercalated Li(4)Ti(5)O(12) x tau(-1) (1/T) follows Arrhenius behaviour with an activation energy E(ASAE) of about 0.86 eV. Interestingly, E(ASAE) is comparable to activation energies deduced from conductivity measurements (0.94(1) eV) and from SLR measurements in the rotating frame (0.74(2) eV) rather than from those performed in the laboratory frame, E(A)(low-T) = 0.26(1) eV at low T.

The microscopic Li diffusion parameters in the lithiated spinel Li4 + xTi5O12, which is on its way to become a commercially used anode material in Li ion batteries, are probed for the first time via nuclear magnetic resonance spectroscopy.

Diffusion in solids D 4000Ultraslow Li Diffusion in Spinel-Type Structured Li4Ti5O12 -A Comparison of Results from Solid State NMR and Impedance Spectroscopy. -Li diffusion in pure-phase microcrystalline Li4Ti5O12 with an average particle size in the µm range is characterized by 7 Li solid state NMR spectroscopy using spin-alignment echo and spin-lattice relaxation measurements between 318 and 423 K. The slow Li diffusion in non-intercalated Li4Ti5O12 follows Arrhenius behavior with an activation energy of about 0.86 eV. 7 Li spin-alignment echo NMR is especially useful for the characterization of Li dynamics in materials relevant for applications in seconary Li ion batteries.-(WILKENING*, M.; AMADE, R.; IWANIAK, W.; HEITJANS, P.; Phys. Chem.

Spinel-type structured Li4+xTi5O12 (0 6 x 6 3 ) is actually one of the most promising anode materials for Li ion batteries. In its nanostructured form it is already used in some commercially available Li ion batteries. As was recently shown by our group (Wilkening et al., Phys. Chem. Chem. Phys. 9 (2007) 1239), Li diffusivity in microcrystalline Li4+xTi5O12 with x = 0 is rather slow. In the present contribution the Li conductivity in nanocrystalline samples of the electronic insulator Li4Ti5O12 prepared by different routes is investigated using impedance spectroscopy. The mean crystallite size of the samples is about 20 nm. The ionic conductivity of nanocrystalline Li4Ti5O12 obtained by mechanical treatment is higher by about two orders of magnitude compared to that found for a material which was prepared following a sol-gel method. The latter resembles the behaviour of the microcrystalline sample with an average particle size in the μm range rather than that of a nanocrystalline ball milled one with a mean crystallite size of about than 20 nm. The larger conductivity of the ball milled sample is ascribed to a much higher defect density generated when the particle size is reduced mechanically.

≤ x ≤ 3) Measured by 7 Li Solid State NMR. -(WILKENING*, M.; IWANIAK, W.; HEINE, J.; EPP, V.; KLEINERT, A.; BEHRENS, M.; NUSPL, G.; BENSCH, W.; HEITJANS, P.; Phys. Chem. Chem. Phys. 9 (2007) 47, 6199-6202; Inst. Phys. Chem. Elektrochem., Univ. Hannover, D-30167 Hannover, Germany; Eng.) -Schramke 09-012