Transition Metal Disulfide Cathode Materials for Thermal Batteries: Iron Disulfide, Cobalt Disulfide, and Nickel Disulfide
Thermally activated batteries occupy a specialized class of primary electrochemical power sources in which the electrolyte remains solid and substantially nonconductive during storage and becomes ionically conductive only after thermal activation. Transition metal disulfides have played a central role in the development of these systems because they combine high electrochemical capacity with thermal stability and compatibility with molten salt electrolytes. Iron disulfide, FeS₂, cobalt disulfide, CoS₂, and nickel disulfide, NiS₂, are among the most extensively investigated sulfide cathode materials for lithium based thermal batteries. Although the three compounds share related pyrite type structures, their thermal stability, electronic behavior, discharge mechanisms, polarization characteristics, and active material utilization differ substantially. These differences make cathode selection dependent on the operating requirements of the battery rather than on a single material property. This article reviews the role of transition metal disulfides in thermal batteries, compares the characteristics of FeS₂, CoS₂, and NiS₂, and examines how phase purity, stoichiometry, particle characteristics, and thermal behavior can influence cathode performance.