Morphology-controlled LiMn0.9Fe0.1PO4 nanoplatelets as high performance cathode material for lithium ion batteries have been synthesized via a simple ascorbic acid-assisted solvothermal process in water-ethanol solvent. The phase structure and morphology of the products were characterized by XRD, SEM and TEM. The results reveal that decreasing the crystallite size along b-axis direction and increasing the surface area of (010) plane can shorten Li+ diffusion path and increase the electrode reaction activity. The LiMn0.9Fe0.1PO4 nanoplatelet holds the high capacity of 145 mA h g−1, 134 mA h g−1, 119 mA h g−1, 97 mA h g−1 and 68 mA h g−1 at 0.1 C, 0.5 C, 1 C, 5 C and 10 C respectively, and it can retain 75% of the initial reversible capacity even after 100 cycles at 10 C rate.