Carbon layers with microporous structures fine-modulated by naphthalene (NAP) were prepared to coat on LiFePO4, aiming to enhance the Li+ diffusion coefficient for Li-ion batteries. Characterized by BET, XRD, TEM, EIS, etc., it is indicated that in the presence of NAP, the carbon-coated LiFePO4/C-NAP composites have the enlarged micropore size of 1.66 nm and the enhanced Li+ diffusion coefficient of 2.83 × 10−12 cm2 s−1, which is about five times higher than that of LiFePO4/C prepared in the absence of NAP. At a high rate of 20 C, the discharge capacity of the LiFePO4/C-NAP is up to 120.1 mA h g−1 and maintains a good retention rate of 93.2% after 400 cycles. It is suggested that the NAP-modulated carbon coating is a promising route to accelerate the Li-ion diffusion rate and enhance the electrochemical performance for lithium ion batteries.