The effects of chemical composition of adsorbed molecular layers on lithium electrode/polymer electrolyte interface stabilization

Previous work in our laboratory has shown that the adsorption of self-assembled molecular layers on a polymer electrolyte surface can make the interface between the electrolyte and a lithium metal electrode more stable and can hinder the growth of the type of passivation layer that inhibits ion movement between the electrode and electrolyte. This work is concerned with the effect that the molecular composition of the adsorbed layer has on interface stability. Several compounds of the form R---(CH2CH2O)---H have been found to adsorb on the surface of the polymer electrolyte and stabilize the interface. It was found that the R group could be a long, straight hydrocarbon tail capable of forming an ordered self-assembled structure or a branched hydrocarbon or a siloxane with bulky hydrocarbon groups that form a brush-type structure. Molecules of the form R---OH and R---COOH, where R was a long, straight-chain hydrocarbon, would adsorb but appeared to have much disorder in their hydrocarbon chains. It is proposed that this disorder results from a low adsorption density that results in regions where the lithium metal can come in direct contact with the polymer electrolyte causing reactions that promote interface destabilization.