During the charge-discharge cycles of the lithium-ion battery, as the concentration of lithium increases in the electrode particles, the expansion of the particles leads to the generation of diffusion-induced stress, resulting in internal resistance and capacity degradation. A three-dimensional electrochemical-mechanical model is developed at the particle level for a LiMn2O4/Graphite battery, which has bridged the stress-strain relation with the lithium diffusion and transportation process. Firstly, the electrochemical part is carried out at the electrode particles to analyze the lithium concentration and electrochemical reaction, it can be concluded that the behavior of lithium-intercalation/de-intercalation follows the principle of "proximity"-the closer the distance between the positive and negative particles, the priority is to achieve lithium-intercalation/de-intercalation. Secondly, the solution of the first step is used to calculate the stress in the graphite particles during the discharge process, the results show that as the lithium concentration increases, the particles expand and stress is generated inside the particle and in-between particles, and there displays larger von Mises stress at the connection between particles, which can be inferred that the sufficient stress will cause cracking, pulverization, fracture of the electrode material, thus leading to increase in internal resistance and capacity degradation. (C) 2019 The Electrochemical Society.