Abstract
A study of charge cycling at the Li/poly[bis(2,3‐di‐(2‐methoxyethoxy)propoxy)phosphazene] interface is reported. Irreversible processes occurring at the Li/solid polymer electrolyte interface have been characterized by using high‐sensitivity dilatometry and electrochemical impedance spectroscopy (EIS) as a function of cycle number. The volume of a Li/solid polymer electrolyte/Li laminate initially increases with cycle number but then attains a steady state after approximately 450 cycles. The impedance, however, is found to remain essentially constant throughout the entire cycling regime and to be essentially resistive (nonreactive) at frequencies below 10 kHz. A point defect model has been developed to interpret the mechanism of the interfacial charge‐transfer processes in terms of the interstitial transfer of 
through a corrosion product layer that forms on the metal surface.