AC impedance study on the interface of lithium and polymer electrolyte based on lithium-N(4-sulfophenyl) maleimide

The properties of the interface between lithium electrode and polymer electrolyte, poly[lithium-N(4-sulfophenyl) maleimide-co-methoxy oligo(ethyleneoxy) methacrylate] with single lithium ionic conduction, have been investigated by A.C. impedance technique. The impedance spectrum for stainless steel electrode shows a semicircle and a straight line, while that for lithium electrode has two separate imperfect semicircles and a spur. This difference suggests that a passivation layer has formed between the interface of the Li/polymer electrolyte. The dependence of the impedance spectra on storage time and temperature has been interpreted using an assumed equivalent circuit. It is revealed that the passivation layer is composed of a combination of solid inorganic and polymeric salts resulting from the reactions of lithium metal with the residual moisture and the polymer electrolyte, and has the characteristics of ionic conductive behavior. It grows rapidly on the surface of the lithium electrode during the initial period after the assembly of cells. The growth of the passivation layer will affect the nature of the polymer electrolyte and lead to an increase in the bulk resistance of the polymer electrolyte. Using the impedance spectra of cells with the stainless steel electrode, the dielectric property of the polymer electrolyte has also been studied. (C) 1998 Elsevier Science B.V. All rights reserved.