Sodium nickel chloride (Na-NiCl₂) batteries are gaining growing attentions as a strong potential contender for advanced electric vehicle (EV) and stationary energy storage system (ESS) applications. The cathode compartment of a Na-NiCl₂ battery features by a mixture of solid NaCl and Ni granules impregnated with a liquid NaAlCl₄ catholyte. During charge-discharge cycles, complicated electrochemical reactions take place, including transportation of Na⁺ ions through NaAlCl₄ catholyte, the dissolution/coarsening of NaCl particles, formation/decomposition of NiCl₂ layers on the active Ni surface, and electron transport through the Ni granules. We are developing advanced Na-NiCl₂ batteries that operate at relatively lower temperatures of below 200 °C to minimize its cell degradation typically observed at high operation temperature (over ~270 °C) and to enable application of simple and cheaper polymer seals for cell manufacturing. However, the diffusion and the ionic migration kinetics of active Na⁺ ions are restricted at the lower temperatures that may limit cell performance. In this presentation, we introduce a multi-physics continuum computational model to capture the electrochemical behaviors of planar lower temperature Na-NiCl₂ batteries. The computational results will elucidate impacts of (i) cell operation temperatures, (ii) current densities, and (iii) cathode dimensions on the electrochemical performance of prototype planar Na-NiCl₂ cells. The developed prediction model is expected to provide a useful guideline for the experimental fabrication of advanced Na-NiCl₂ batteries with maximized cell performance at relatively lower temperatures.