The heat generation in a battery cell is determined by the battery chemistry and kinetics. The battery operation conditions and design parameters have a strong influence on the kinetics. To study the relationships among these parameters, a coupled thermo-electrochemical model for a basic lithium (Li) ion battery cell has been developed. The model was implemented for a Li x C6|LiPF6 (EC/DMC)|Li y Mn2O4 cell. The temperature dependence of six sets of physical properties relevant to the reaction rate and Li+ transport was investigated. The model was validated against literature data. The predicted heat generation rates were within the range of available experimental results. The model was used to evaluate the influence of active particle size and component thickness on the heat generation rate and battery performance. The results revealed that while batteries with a thin component thickness had a lower temperature rise and better battery utilization, the effect of the particle size was not monotonic across the discharge rates.