Raman and NMR analysis of LiClO4 concentrated solutions in ethylene carbonate propylene carbonate

A comparative Raman and C-13-NMR study has been performed on LiClO4 concentrated solutions in ethylene carbonate (EC)-propylene carbonate (PC), which are of interest for electrochemical devices like secondary lithium batteries. A phase transition has been detected near a ratio N = [Li+]/[EC + PC] congruent to 0.5. Below this threshold, Li+ ions are relatively free to move and are solvated by EC and PC with a coordination number, n, which approaches similar to 2. In more concentrated solutions the cations seem to form a complex by ''sandwiching'' an EC and a PC molecule.