The present invention relates to a thermal energy storage material (TESM) system (and associated methods). The TESM system comprises i) a container having a wall surface; and ii) a TESM in at least partial contact with the wall surface. The TESM may include, consist essentially of, or consist of a metal containing compound comprising at least two different metal cations and one or more polyatomic anions. The at least two metal cations may include lithium cations. The TESM may have a liquidus temperature, TL, from about 100° C. to about 250° C. The TESM may exhibits a heat storage density from 300° C. to 80° C. of at least 1 MJ/l. The TESM system may be free of water. If any water is present in the TESM system, the water concentration preferably is less than about 10 wt. %. Preferably, the TESM system is generally resistant to corrosion at temperatures of about 300° C.