Abstract: Two commercial conductive additives, carbon black (super P, SP) and vapor grown carbon fibers (VGCFs), were used to construct an effective conducting network in the cathode of commercial LiFePO4 lithium ion batteries (LIBs). Results suggest that the LIB with SP possesses a higher discharge capacity than that with VGCFs with the same mass fraction of the additives. The high-rate capacity of LIB with SP is much higher than that with VGCFs. Furthermore, the LIB with a mixture of these two additives has an apparently improved performance in low and high rate discharge capacity compared with the LIBs with a single component additive with the same mass fraction due to the synergetic effect. The same conclusion can be reached for the larger-capacity batteries (10 Ah or 50 Ah packs). Therefore, the use of two different fillers is important for the high power LIBs used in the electric vehicle and mass energy-storage industry.