Monodispersed and uniform cubic LiMn2O4 with side length of 5.0 μm denoted as CB and spherical LiMn2O4 with different diameters (2.0, 3.5, 8.0 μm) denoted as SS, MS, BS respectively are prepared through a controllable precipitation of precursors MnCO3 and a followed melt-impregnation process. Studies show that the electrochemical performance of LiMn2O4 samples with spherical morphology are better than those of the cubic one. Moreover, the spherical LiMn2O4 (MS) with middle size (3.5 μm in diameter) has the best electrochemical performance among three spherical samples instead of the smallest spherical LiMn2O4. The determined apparent lithium ion diffusion coefficients of prepared samples decrease in the order of MS > SS > BS > CB and their values are in the range of 10−9.5–10−11.5 cm2 s−1 and 10−8.0–10−10.5 cm2 s−1 from PITT and CITT respectively. This trend matched well with the electrochemical performances of the four cathode materials. This observation can be addressed to the fact that the middle size spherical particles balance the contradictory of diffusion length in solid phase and particle agglomeration, which lead to perfect contacts with the conductive additive, considerable apparent Li-ion diffusion rate and the best performance of MS LiMn2O4.