A uniform carbon coated LiFe0.15Mn0.85PO4 (LFMP/C) cathode material is synthesized by a surfactant-assisted, highly reproducible and energy-saving solid state method using a bimetallic oxalate (Fe0.15Mn0.85C2O4) precursor. The obtained LiFe0.15Mn0.85PO4/C composite is characterized by X-ray diffraction (XRD), Raman spectrum, elemental analysis (EA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The experimental results demonstrate that the oleic acid as a surfactant, for the scale preparation of LFMP, plays a critical role in controlling size of the obtained composite. The LiFe0.15Mn0.85PO4/C exhibits high specific capacity and good rate performance. It delivers initial discharge capacities of 156.5, 142.5, 129.0 and 103.0 mAh g−1 at 0.05, 0.1, 0.5 and 1C, respectively. Moreover, it shows good cycle stability at both room temperature (25 °C, 89% and 88% capacity retention after 250 and 500 cycles at 0.5 and 1C rates, respectively) and elevated temperature (55 °C, 80% capacity retention after 200 cycles at 0.5C rate). The significantly improved rate and cycling capability of the LiFe0.15Mn0.85PO4/C is attributed to the uniform carbon coating layer on the primary particles, the conductive network provided by the carbon between the LiMn0.15Fe0.85PO4/C particles and the sufficient pores formed in the LiFe0.15Mn0.85PO4/C aggregates.