Thermal energy storage materials

The present invention relates to a thermal energy storage material (TESM) system (and associated methods) that reproducibly stores and recovers latent heat. The Thermal energy storage material system comprises i) at least one first metal containing material including at least one first metal compound that includes a nitrate ion, a nitrite ion, or both; and ii) at least one second metal containing material including at least one second metal compound. The thermal energy storage material system may water. If any water is present in the thermal energy storage material system, the water concentration should be less than about 10 wt. %. The thermal energy storage material has a liquidus temperature, TL, from about 100° C. to about 250° C. and exhibits a heat storage density from 300° C. to 80° C. of at least about 1 MJ/l, so that upon being used in a system that generates heat, at least a portion of the heat is captured and stored by the thermal energy storage material and subsequently released for use. The thermal energy storage material system is generally resistant to corrosion at temperatures of about 300° C. Exemplary metal compounds include one or more cations selected from the group consisting of Li, Na, K, Be, Mg, Ca, Al, and Ga.