A mathematical model that includes an anode (carbon) decomposition reaction has been used to predict the temperature of a lithium-ion cell during medium- and high-rate discharge conditions. This work describes how various design parameters and the activation energy for the decomposition reaction of the anode (carbon) affect the predicted temperature of a LixC6/LiyNiO2 cell. The predicted results show that the particle size in the negative electrode (assumed here to be petroleum coke) is an important parameter for predicting the temperature of the cell.