Lithium diffusion coefficient in LiMn2O4 thin films measured by secondary ion mass spectrometry with ion-exchange method

In this study, the lithium tracer diffusion coefficient (DLi∗) in spinel-type LiMn2O4 thin films is measured by secondary ion mass spectroscopy (SIMS) in the temperature range from 200 to 550 °C. An ion-exchange method is employed to prepare diffusion couples consisting of the stable isotopes 6Li and 7Li. The isotope profiles were measured by SIMS analysis to determine DLi∗ in the LiMn2O4 films. The DLi∗ value was 1.4 × 10−10 cm2/s at 300 °C and the activation energy was 0.52 eV, which is consistent with that of bulk LiMn2O4. The extrapolated value of DLi∗ at 25 °C was on the order of 10−14 cm2/s, which is smaller than the chemical diffusion coefficient of LixMn2O4 measured by electrochemical methods. The temperature dependence of DLi∗ can be explained by the vacancy diffusion model, in which the extrinsic and intrinsic regions of diffusion exist in the low- and high-temperature regions, respectively.