Abstract: Thermal energy storage mixture and heat storage/release device using same. The mixture including 45% by weight of compounds from a first class and 10% by weight of compounds from a second class. The first class having a melting temperature of at least 180° C. and a fusion enthalpy of at least 150 MJ/m3. The first class including ?-lactose, myo-inositol, cellobiose, sodium acetate and sodium propionate, in which the at least one compound always includes ?-lactose or sodium propionate or a mixture thereof. The second class having a melting temperature less than 180° C. The compound(s) of the second class being totally miscible, both in solid and liquid phase, with the compound(s) of the first class. The second class including organic compounds made of carbon, hydrogen and oxygen, of sodium salts of carboxylic acids and of potassium salts of carboxylic acids.