Abstract: Two conductive additives, carbon black (Super-P) and vapor-grown carbon fibers (VGCFs), were used in 2.5 Ah Li ion batteries using LiCoO₂ as the cathode and a SiO/C composite as the anode. The electrode shape, peel strength, electrolyte absorption, electrolyte storage capacity, volume change and the electrochemical performance were investigated. Results indicate that both batteries have high energy densities (more than 600 Wh/L), but the batteries with VGCFs have the better low temperature performance, longer cycle life, higher rate capability and lower volume expansion, which is ascribed to the superior conductive network formed by the VGCFs.