Using amorphous FePO4 (a-FePO4) nanoparticles with a high purity, a narrow size distribution and good dispersion, we successfully developed a new strategy to generate a uniformly dispersed a-FePO4-CNT nano-composite using the interface interaction between surface-modified a-FePO4 and CNT dispersion under mild sonication. The uniformly dispersed a-FePO4-CNT nano-composite exhibited the best performance and long-term stability as a cathode material in a lithium-ion battery compared to previously reported results. The developed nano-composite could deliver a theoretical specific capacity at 0.1 C, 162 mAh g−1 at 1 C and 117 mAh g−1 at 5 C. No capacity fading was observed at 1 C after 500 cycles, and nearly 90% of the initial discharge capacity could be retained at 5 C after 2000 cycles. This study confirms the validity of the proposed strategy to construct a cathode structure, and also describes the potential of a-FePO4 for building high-power energy-storage and conversion systems.