Enthalpy of formation of intermetallic compounds from the Li–Si system

With the use of the solution calorimetric method, the energetic effect of solutions of Li and the Li13Si4, Li7Si3 and Li12Si7 intermetallic compounds in the acetic acid were measured and next the formation enthalpies of the compounds were calculated. The intermetallic compounds were prepared by means of melting lithium and silicon in a glove-box under the protective atmosphere of high purity argon. The obtained compounds were X-ray analyzed in order to confirm theirs structure. The TEM analysis of the precipitate obtained after the dissolution of the phases in the acetic acid showed that it was pure silicon. The measured heat of the reaction of Li in the acetic acid equals −261.1 ± 1.6 kJ/mol and this value was applied in the calculations. The values obtained for the formation enthalpy of the compounds are as follows: −30.4 ± 0.8 for Li13Si4, −29.4 ± 1.0 for Li7Si3 and −25.6 ± 1.9 for Li12Si7.