This paper discusses the FIF-infrared (IR) and NMR spectroscopy results of a mesoporous silica (SBA-15) composite poly(ethylene oxide) (PEO) solid lithium polymer electrolyte. The changes in COC, CH, and ClO4 stretching IR vibrational modes indicated a combination of multiple interactions through Lewis acid-base reactions which interrupt the PEO crystalline structure. Higher salt disassociation by SBA-15 is also apparent from ClO4 vibrational band mode. NMR studies indicated three types of Li ion environments; the first one is Li ions within the conventional amorphous PEO, the second is Li ions on the surface of mesoporous SBA-15 and the third is Li ions trapped along with PEO in the nano-tubular channels of SBA-15. Annealing leads to interaction of more PEO and lithium ions with the SBA-15 and free ions for conduction, as reflected in the 7 Li variable temperature (VT)-NMR measurements and variable temperature ion conductivity. (c) 2005 Elsevier B.V. All rights reserved.