Lithium ion chemical diffusion coefficients in 6LiMn2O4 thin sputtered films (∼2μm) were determined by the depth profiles of 7Li concentration after adopting the potential step in 7LiClO4/propylene carbonate solution by using secondary-ion mass spectrometry (SIMS). Lithium chemical diffusion coefficient via bulk (D bulk) and grain boundary diffusion coefficient normalized with width (dD gb) were determined as 1.23×10−15 m2 s−1 and 6.55×10−20 m3 s−1, respectively.