Using self-assembled monolayers to inhibit passivation at the lithium electrode polymer electrolyte interface

This work investigates the use of surface chemistry to modify the lithium e lectrode/polymer electrolyte interface by placing a molecular layer, most l ikely in the form of a self-assembled monolayer (SAM), of H-(CH2)(32)-(CH2- CH2-O)(10)-H onto the surface of PEG, poly(ethylene oxide), electrolyte fil ms. It is proposed that the PEG-like "head" of the molecule above preferent ially orients itself to absorb onto the PEO electrolyte, leaving the hydroc arbon CH2 "tail" to self-assemble. SAM placement was confirmed using attenu ated total reflection FTIR spectroscopy and wetting studies, and AC impedan ce measurements were used to investigate the passivating layer development. Extended time period studies of untreated polymer films in contact with li thium exhibited the rapid rise of an interfacial passivating layer whose re sistance overtook that of the bulk electrolyte. Similar studies demonstrate d that samples with SAMs actually had a small increase in ion conductivity and developed interfacial passivation much slower, supporting the assertion that SAMs could be used to deter the formation of a barrier to Li+ transpo rt during cycling of lithium polymer batteries. (C) 1999 Published by Elsev ier Science B.V. All rights reserved.