The discharge characteristics of a Li/LiyCoO2 cell were simulated by numerical calculations. Based on the program proposed by Newman's group, the change in entropy due to lithium-ion insertion into the active materials was introduced into the open-circuit potential (OCP) for more practical applications. The OCP of LiCoO2 (y = 1) at a full-discharge state was 3.82 V, which was determined from the original program. However, it should show a rapid decrease to minus infinity when discharge is complete (y = 1), which is due to the introduced entropy term. In addition, the local use of active materials across the LiyCoO2 electrode was not uniform, whereas the original program showed a constant value throughout the electrode. Based on the present results, the introduction of an entropy term to the OCP of LiyCoO2 works reasonably well for more practical applications. (C) 2007 Elsevier B.V. All rights reserved.