Based on the equation of i=av b between the current (i) and scan rate (v), the value of b is determined by the slope of log (i) and log (v) curve, while the b-value close to 1.0 signifies that the electrochemical process is controlled by the capacitive response, whereas b-value close to 0.5 indicates the diffusion process is dominating. The b-value from the anodic or cathodic current at 0.8 V vs. Li/Li + is calculated to be 0.942 or 0.916 (Fig. ), respectively. Interestingly, the b value is between 0.5 and 1, much close to 1, indicating that the capacitive effect may occupy the main parts of the charge storage behavior. In general, the capacitance process includes adsorption capacitance and pseudocapacitance . Actually, materials with pseudocapacitive properties also participate in the diffusion process . Thus, the detailed quantification of capacitive contribution is measured according to the Dunn's method to acquire the actual ratio and the following equation mV s -1 ), while the pseudocapacitive contribution is 35.5%, 28.0%, 21.6%, 14.8%, 11.8%, 8.0% or 5.2%. The ratio of capacitive contribution is quite limited by the adsorption process, indicating that the pseudocapacitive process plays a small part in the charge storage behaviors. The first galvanostatic charge-discharge curve in Fig. shows three plateaus at 1.1 V, 0.8 V and 0.2 V vs. Li/Li + corresponding to the first CV cathodic process. The first discharge or charge capacity is 746 mAh/g or 529 mAh/g, respectively, which would result in an initial coulombic efficiency of 70.9%. A similar behavior has been reported for Fe-based anodes during lithium insertion . The coulomb efficiency of 25 cycles is in the range of 82%, which can be seen from Supplementary Fig. . Specifically, after 1st cycle of SEI film formation, only the discharge time or discharge capacity from the 2nd cycle to the 4th cycle decreases slightly, while the discharge time or discharge capacity from the 5th cycle to the 25th cycle is almost unchanged. This clearly shows that no side reaction or irreversible faradaic deposition occurs after the successful formation of the SEI film.