It is well-established that the micro-sized LiFePO4 exhibits very poor rate capability, whereas nano-sized LiFePO4 displays very excellent rate capability. Thereby, kinetic behavior of nano-sized LiFePO4 is attracting wide attention. Herein, it is reported that nano-sized LiFePO4 can realize the fast charge/discharge of 100 C with limited carbon additive. Most importantly, it is discovered that the capacity of LiFePO4 observed above 3.5 V (vs. Li/Li+) and below 3.4 V (vs. Li/Li+) is mainly due to the pseudo-capacitive behavior rather than single-phase Li-intercalation, indicating that there is only very small potential difference (100 mV, 3.4–3.5 V) between the single-phase transformation and two-phase equilibrium. Also cycle-life test, combining with TEM observations, demonstrates that the crystalline-to-amorphous transformation in part of nano-LiFePO4 particles during cycling process can result in the change of voltage at the end of charge/discharge.