8Li β-NMR study of epitaxial LixCoO2 films

Abstract

In order to investigate the diffusive motion of Li+ in a thin film electrode material for Li-ion batteries, we have measured β-NMR spectra of 8Li+ ions implanted into epitaxial films of Li0.7CoO2 and LiCoO2 in the temperature range between 10 and 310 K. Below 100 K, the spin-lattice relaxation rate (1/T1) in the Li0.7CoO2 film increased with decreasing temperature, indicating the appearance and evolution of localized magnetic moments, as observed with μ+SR. As temperature is increased from 100 K, 1/T1 starts to increase above ∼ 200 K, where both Li- NMR and μ+SR also sensed an increase in 1/T1 due to Li-diffusion. Interestingly, such diffusive behavior was found to depend on the implantation energy, possibly because the surface of the film is decomposed due to chemical instability of the Li0.7CoO2 phase in air. Such diffusive behavior was not observed for the LiCoO2 film up to 310 K.