Development of an equivalent-circuit model for the lithium/iodine battery

The lithium/iodine battery is the most widely used power source for implantable cardiac pacemakers. While the average power demands of pacemakers are very low, the instantaneous power requirements can challenge the capabilities of this high impedance battery. Thus, there is a need to predict the transient-response behavior of new battery designs. Impedance spectroscopy was used to characterize the behavior of a variety of cell designs as a function of cell design, depth-of-discharge, and current density. An equivalent-circuit model was developed in terms of the physical elements which contribute to electrical resistance, capacitance, and electrochemical polarization. The transient-response predicted by this simple equivalent-circuit model was compared to pulse data from actual batteries and found to be in excellent agreement.