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

摘要

In this study, the lithium tracer diffusion coefficient (Ai') in spinel-type LiMn2O4 thin films is measured by secondary ion mass spectroscopy (SIMS) in the temperature range from 200 to 550 degrees C. An ion-exchange method is employed to prepare diffusion couples consisting of the stable isotopes Li-6 and Li-7. The isotope profiles were measured by SIMS analysis to determine D-Li* in the LiMn2O4 films. The Du* value was 1.4 x 10(-10) cm(2)/s at 300 degrees C and the activation energy was 0.52 eV, which is consistent with that of bulk LiMn2O4. The extrapolated value of D-Li(*) at 25 degrees C was on the order of 10(-14) cm(2)/s, which is smaller than the chemical diffusion coefficient of LixMn(2)O(4) measured by electrochemical methods. The temperature dependence of Du* 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.