Structural and dynamical properties of the electrolyte system ethylene carbonate-Li+ are studied. A high-Level ab initio study of the geometry and vibrational spectrum has been performed both for an isolated molecule and for small clusters including the lithium ion. The ethylene molecule is found to be nonplanar in all instances, and an assignment of vibrational modes is proposed on this basis. It is shown that the lithium ion induces substantial blue- and redshifts, mainly on the ring- and carbonyl-stretching modes. These issues have also been studied in the liquid phase for the first time, and for that purpose, a new intramolecular force field has been developed. It is shown that this intramolecular potential satisfactorily reproduces a broad range of features, allowing us to interpret the shifts measured experimentally for the molecules within the first solvation shell of the ion. Particularly, the broadening of the carbonyl band found experimentally is the result of an ion-induced redshift, obscured by the presence of Fermi resonances. Moreover, the study of the shifts as a function of solvation number supports a 4-coordinated solvation shell.