Charge and discharge properties of a graphite/SiO_x composite electrode were studied over a wide range of charge/discharge rates (1/20 to 5 C) for use in automotive applications. The graphite/SiO_x (90/10 by weight) composite electrode gave a high reversible capacity (453 mAh·g⁻¹), and showed a good capacity retention at a low rate of 1/20 C. However, the capacity decreased significantly on cycling at a high rate of 2 C. From the analysis of the charging and discharging processes, it was found that the charging reaction occurs predominantly at SiO_x particles initially at higher potentials and then proceeds at graphite particles at lower potentials to be fully charged. This tendency was also supported by a dependence of the activation energy of the charge transfer reaction on the state of charge (SOC) estimated by ac impedance analysis. Because the composite electrode contains only 10% SiO_x, the current was excessively concentrated to the SiO_x particles at the initial state when charged at high rates. This caused crack formation in SiO_x particles, and the resulting contact loss between particles was considered as the reason for the observed poor cycleability at 2 C.