Details on the structure and transport characteristics of the solid polymer electrolyte polyethylene oxide (PEO)/lithium salt (LiClO4) modified by novolac phenolic resin are presented here. From IR spectra it could be concluded that complex formation occurred through multiple interactions between the ether oxygen of PEO-lithium, phenolic lithium, and the phenolic ether oxygen of PEO. The free hydroxyl band in phenolic reflected that phenolic closely interacted with both the PEO polymer and ionic salt. With increasing salt content in PEO, the vibration band corresponding to the ClO4- anion (similar to623 cm(-1)) displayed growth of a shoulder at similar to635 cm(-1), suggesting the formation of Li+...ClO4- ion pairing. However, in the presence of phenolic, ion-pairing formation was effectively suppressed, which suggested that the phenolic moiety facilitated a greater degree of LiClO4 salt dissociation. Activation energy analysis revealed two conducting pathways: one through the amorphous PEO and the other through the PEO/phenolic amorphous matrix. The high ion conductivity originated from effective salt dissociation and the establishment of a new conduction network formed by PEO and phenolic. Furthermore, the structural modification also extended the thermal stability and mechanical strength of the solid polymer electrolyte composite. (C) 2004 Wiley Periodicals, Inc.