Characterization of self-assembled molecular layers at the polymer electrolyte/lithium electrode interface

Formation of a passivation layer at the lithium electrode/electrolyte inter face is a major concern for lithium polymer batteries. This work investigat es the formation of self-assembled molecular layers on the polymer electrol yte interface. Previous work in our laboratory has shown that these molecul ar layers can greatly slow the passivation process. The molecular layers ar e placed onto the surface of the poly(ethylene oxide), PEG, electrolyte fil ms 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 t o slow or even inhibit interfacial passivation from occurring in lithium sy mmetric cells under an open circuit potential. ATR-FTIR, light microscopy, atomic force microscopy (AFM) and alternating current (ac) impedance spectr oscopy have been used to characterize the molecular layers. AFM data indica te that after adsorption, multiple layers having an average single layer th ickness of 5.5 +/- 0.5 nm are present on the PEO electrolyte surface. (C) 2 000 Elsevier Science Ltd. All rights reserved.