Charging and discharging lithium ion batteries (LIBs) in a matter of seconds to tens of seconds rather than hours can potentially lead to technological breakthroughs and bring about lifestyle changes. This work aims to enable ultrafast Li-ions charge/discharge ability for LIBs by significantly accelerating the diffusion kinetics of Li+ ions and enhancing the electric conductivity in LiFePO4 cathode material. An innovative method was developed to synthesize LiFePO4/C nanocomposite with secondary particles structure containing uniform (20–50nm) and highly crystalline LiFePO4 single nanoparticles which are free from any anti-site defects (e.g. Fe· Li) and uniformly coated by a highly graphitized carbon-shell network with good electronic conduction. The LiFePO4/C material was formed from a FePO4·xH2O/poly(furfuryl alcohol) nanocomposite, which was prepared through a self-regulated in situ polymerization restriction method, followed by a rapid wet-chemistry lithiation (H+/Li+ ion exchange) and subsequent calcination. Benefiting from the ultra-small size of the LiFePO4 nanoparticles, absence of Fe· Li defects, and a continuous 3D carbon network, the LiFePO4/C nanocomposite demonstrated ultrafast lithium-storage rates when used as a cathode material in lithium half-cells, which required only 21.6s to reach a complete discharge at a rate of 150C while still maintaining a high specific capacity of 95.4 mAh g−1.