The solution-reaction calorimetric method was used for the determination of the formation enthalpy of the Li22Si5 intermetallic compound and the heat of the reaction of the Li-component with an acetic acid bath. The phase was prepared in a glove box with high purity argon protective atmosphere. The phase was homogenized and then analyzed by means of the X-ray diffraction technique. Also, the topography analysis was performed with the use of a scanning electron microscopy (SEM), whereas the microstructure analysis was performed by means of a transmission electron microscopy (TEM). The phase analysis was also run by the selected area electron diffraction pattern (SAEDP). The experiments in the calorimeter were carried out at room temperature with acetic acid as the calorimetric solvent. The enthalpy of the lithium's reaction with the acetic acid was measured and it equaled −261.1±1.6kJ/g·atom. The formation enthalpy value Δf H for the Li22Si5 compound was equal to −24.4±3.0kJ/g·atom.