Investigation of the position of Li+ ions in a polyacrylonitrile-based electrolyte by Raman and infrared spectroscopy

The Raman spectra of polyacrylonitrile (PAN) and/or lithium perchlorate (LiClO4) complex containing plasticizer ethylene carbonate and the infrared spectra of the polymer electrolytes with different mass ratios of PAN to LiClO4 have been studied. It has been found that the lithium ions strongly interact with the CN groups of PAN. However, at the ordinarily used content, say, the concentration of Li+ ions is as low as 5%, because of the high intensity of the characteristic vibration of the CN group of PAN, it is very difficult to observe the interaction between the ions and the molecules. When the content of LiClO4 is raised to a certain extent, this interaction can be detected by way of Raman and IR spectroscopy. In both the Raman and IR spectra of the system of EC/PAN/LiClO4 with various mass ratios of PAN and LiClO4, a striking shoulder was observed at about 2270cm−1. By comparing the spectra of the system with that of ECPAN and ECLiClO4, the new shoulder was assigned to the interaction between Li+ ions and the CN groups of the PAN molecules.