Developing rechargeable lithium ion batteries with fast charge/discharge rate, high capacity and power, long lifespan, and broad temperature adaptability is still a significant challenge. In order to realize the fast and efficient transport of ions and electrons during the charging/discharging process, a pure and well-crystallized LiMn0.8Fe0.2PO4 cathode material is directly synthesized via co-precipitation method at ambient pressure and 130 °C. Nano-LiMn0.8Fe0.2PO4/C with 5.7 wt% conductive carbon delivers a discharge capacity of 160.6 mAh g−1 at 0.05 C, close to the theoretical value (170 mAh g−1). Even at 10 C, 20 C and 50 C, stable capacities of 113 mAh g−1, 102 mAh g−1 and 83 mAh g−1 are obtained, respectively. The discharge capacity at −15 °C is as high as 97 mAh g−1 at 0.1 C. The excellent high-rate and low-temperature performances of nano-LiMn0.8Fe0.2PO4/C effectively promote its practical usage in lithium-ion batteries.