The reaction current density is an important process parameter of lithium-ion battery, significantly influencing its electrochemical performance. In this study, aimed at the discharge process of lithium-ion power battery, an electrochemical-thermal model was established to analyze the distribution of the reaction current density at various parts of the cathode and its evolution with the time of discharge, and to probe into the causes of distribution and evolution. The investigation revealed that the electrochemical-thermal coupled model showed more accurate compared to the single electrochemical model, which was more obvious in high rate discharge. The results demonstrated that the conductivity of solid and liquid-phases was an important factor affecting the distribution of the reaction current density. Moreover, the uniformity of the distribution of the current density was related to the rate of utilization of the active materials in the electrodes. By optimizing the porosity and thickness of the electrode, not only the distribution of the current density was improved, but also the rate of utilization of the active materials in the electrodes and the energy density of batteries were significantly enhanced. (C) 2014 The Electrochemical Society. All rights reserved.