An analytical model is proposed to describe the two-dimensional distribution of potential and current in planar electrodes of pouch-type lithium-ion batteries. A concentration-independent polarization expression, obtained experimentally, is used to mimic the electrochemical performance of the battery. By numerically solving the charge balance equation on each electrode in conjugation with the polarization expression, the battery behavior during constant-current discharge processes is simulated. Our numerical simulations show that reaction current between the electrodes remains approximately uniform during most of the discharge process, in particular, when depth-of-discharge varies from 5% to 85%. This observation suggests to simplify the electrochemical behavior of the battery such that the charge balance equation on each electrode can be solved analytically to obtain closed-form solutions for potential and current density distributions. The analytical model shows fair agreement with numerical data at modest computational cost. The model is applicable for both charge and discharge processes, and its application is demonstrated for a prismatic 20Ah nickel-manganese-cobalt lithium-ion battery during discharge processes.