4V-class olivine C–LiMn1−x Fe x PO4 (x =0 and 0.15) are synthesized by ultrasonic pyrolysis followed by ball milling with AB carbon to evaluate the doping effect of iron. The C–LiMn0.85Fe0.15PO4 shows excellent rate capability having discharge capacity of 150mAhg−1 at 0.5C-rate and 121mAhg−1 at 2C-rate. The capacity retention of the C-LiMn0.85Fe0.15PO4 is 91% after 50 cycles at 55°C whereas C–LiMnPO4 is limited to 87%. The improved electrochemical performance of the C–LiMn0.85Fe0.15PO4 electrode is attributed to the enhanced electrical conductivity caused by tighter binding on the carbon particles with the LiMn0.85Fe0.15PO4 primary particles as well as by the surface coating of carbon on the primary particles.