Abstract: During the charge-discharge process of the lithium ion battery, the electrode particles will expand or contract with the intercalation/deintercalation of the lithium, which will correspondingly generate stresses. Excessive stress will lead to rupture and broken of the electrode materials, resulting in an increase in the battery internal resistance, causing degradation in the cycle performance and capacity, and finally leading to failure of the battery. In this paper, a three dimensional electrochemical-mechanical model of the positive and negative ellipsoid particles is established to obtain the lithium concentration and stress distribution of the particles. The results show that the stress is large at the connection area between the two particles, and the excessive stress will impair the intercalation/deintercalation ability of lithium ions, which causes lower lithium concentration between the negative particles and higher lithium concentration between the positive particles. Furthermore, the radial stress is zero at the surface of the particles, while the maximum radial stress is located at the center of the particle, and the maximum tangential stress occurs at the surface between the two particles.