A simple and effective method has been developed to synthesize a nano-sized LiFePO4/PAS (polyacenic semiconductor) composite. The LiFePO4 particles coated and connected by PAS are uniformly distributed in the range of 50–80nm. The electronic conductivity of this material is as high as 1.2×10−1 S/cm due to the conductive network of PAS. In comparison with the micro-LiFePO4/PAS, the nano-LiFePO4/PAS exhibits much better rate performance. At the 12-min charge–discharge rate, the power and energy densities of the nano-LiFePO4/PAS are shown as 2063W/kg and 412Wh/kg, which are much higher than those of the micro-LiFePO4/PAS (1600W/kg and 320Wh/kg). It is especially notable that the nano-LiFePO4/PAS cathode without adding Super P shows similar electrochemical behaviors with the cathode adding Super P at all C-rates. Thus, such cathode without adding Super P will enlarge both the volume energy density and weight energy density of batteries. In addition, this cathode exhibits an excellent long-term cyclability, retaining over 95.4% of its original discharge capacity beyond 500 cycles at 0.2C rate. These favorable electrochemical performances should be attributed to its nanometric particle size and the high electronic conductivity.