The temperature dependence of the spin-lattice relaxation time, T1 and the line-width of the 7Li nucleus were measured in de-lithiated LixCoO2 (x = 0.6, 0.8, 1.0). Two different relaxation behaviors were observed in the temperature dependence of T1−1 in an x = 0.8 sample. These would have arisen from inequivalent Li sites in 2 coexisting phases; an original hexagonal (HEX-I) and a modified hexagonal (HEX-II) phase in the x = 0.8 sample. This was analyzed by using a phenomenological non-Debye type of relaxation model. Motional narrowing in the line-width was observed in each sample. This revealed that Li+ ions began to move at low temperatures in samples with lower Li contents. It was found that the activation energy associated with Li+ ion hopping in the HEX-II phase was lower than that in the HEX-I phase. The results showed that the HEX-II phase produced in the Li de-intercalation process would be suitable for Li+ ionic diffusion in multi-phase LixCoO2, and it was expected that this would permit fast ionic diffusion. The Li+ ionic diffusion related to phase transitions was considered with regard to 7Li nuclear magnetic resonance results.

7Li NMR Study on Li+ Ionic Diffusion and Phase Transition in LixCoO2. K.Nakamura, H.Ohno, K.Okamura, Y.Michihiro, T.Moriga, I.Nakabayashi, T.Kanashiro: Solid State Ionics, 2006, 177[9-10], 821-6