Manganese oxide material can rapidly store and release low-grade heat without decomposing

https://phys.org/news/2022-04-manganese-oxide-material-rapidly-low-grade.html

"intercalation mechanism, where water molecules are reversibly inserted into a layered material, is very advantageous for heat storage... very fast, reversible and the material's structure is well maintained. Also, oxygen in the atmosphere doesn't degrade the layered manganese oxide crystal and water doesn't dissolve it... irnessite-type... better all-round performance... long lifetime, can reversibly store and release large amounts of heat per unit volume, and rapidly charges and discharges"