Generally, it is well known that the lithium-ion diffusion in olivine Li x FePO4 is correlated with the phase transition dominated by a domino-cascade model instead of a core–shell model. Based on the experiment result, we firstly found that the linear Warburg region of electrochemical impedance spectra should tilt with a small angle of 30° for the domino-cascade model, while the core–shell model should correspond to a traditional angle of about 45°. Considering that the measured Warburg impedance varies along the charge and discharge processes, we firstly proposed a hybrid phase-transition model as a combination of the domino-cascade model and the core–shell model to describe the olivine Li x FePO4. And this hybrid model was possibly attributed to both the strong anisotropy in the bulk of olivine Li x FePO4 and the different properties between the lithiated and delithiated phases. Potentially, this micro-mechanism could be extended to some other two-phase electrode active materials in lithium ion batteries.