The entropy change in Li/C halfcells was measured by electrochemical microcalorimetry. For Li bulk deposition an entropy increase of 165 J/(mol K) was found. It results primarily from desolvation of Li. A coordination number of 4.4 for Li was derived from the reaction entropy. A linear correlation between the intercalation potential of Li in graphite and the entropy of intercalation shows that the change of DeltaS causes the change of the intercalation potential as a function of the charging state.