Polymer electrolytes composed of polyacrylonitrile (PAN), propylene carbonate (PC) and lithium bis(trifluoromethane sulfone imide) (LiTFSI, LiN(CF3SO2)(2)) have been studied by Raman and AC impedance spectroscopy. Impedance study shows that the conductivity of the electrolyte is strongly dependent on the salt content, and a transition from "salt-in-polymer" to "polymer-in-salt" electrolyte is observed when the salt content is very high. This transition has its response in the Raman spectrum and a new component is observed at 2280 cm(-1) involving the interaction between the polymer and ionic cluster [Lim+TFSIn-] (m>n) as well as the 2270 cm(-1) peak related to the nitrile-Li+ interaction. Based on these facts, it is proposed that PAN play distinct roles in the transportation of the ionic species in conventional "salt-in-polymer" electrolyte and in the ''polymer-in-salt" electrolytes.