This paper develops a computational model and applies it to investigate the performance of a rechargeable battery that is comprised of a molten-sodium anode, a NASICON sodium-ion-conducting separator membrane, and a iodine-based cathode. The cathode compartment is comprised of a porous-carbon felt and an aqueous catholyte that supports an iodine redox process. The battery chemistry can be represented globally as 2Na+ +2I− ⇌2Na+I2. The ion transport is represented in terms of a Nernst–Planck formulation that includes four mobile species within the catholyte, Na+, I−, I 3 − , and I2. The charge transfer chemistry is modeled using a Butler–Volmer formulation. The model considers solubility limits and the potential precipitation of NaI and I2. Parameter studies investigate the influences of charge and discharge rates, total elemental iodine loading, and effective conductivity of the carbon-felt cathode.