Formation of a passivation layer at the lithium electrode/electrolyte interface is a major concern for lithium polymer batteries. This work investigates the formation of self-assembled molecular layers on the polymer electrolyte interface. Previous work in our laboratory has shown that these molecular layers can greatly slow the passivation process. The molecular layers are placed onto the surface of the poly(ethylene oxide), PEG, electrolyte films via adsorption from hexane solution and are formed from molecules of the general form H-(CH2)(n)-(CH2-CH2-O)(m)-H. We have studied molecular layers formed from molecules where n equals 29, 32 or 40 and nl is 0, 3, 10 or 41. Based on ac impedance spectroscopy, all molecular layers studied appear to slow or even inhibit interfacial passivation from occurring in lithium symmetric cells under an open circuit potential. ATR-FTIR, light microscopy, atomic force microscopy (AFM) and alternating current (ac) impedance spectroscopy have been used to characterize the molecular layers. AFM data indicate that after adsorption, multiple layers having an average single layer thickness of 5.5 +/- 0.5 nm are present on the PEO electrolyte surface. (C) 2000 Elsevier Science Ltd. All rights reserved.