Using impedance spectroscopy and in situ optical absorption experiments, we have studied the evolution of a lithium electrode/polymer electrolyte interface during aging and cycling. During a period of 3-5 days after assembling a cell, aging has a detrimental effect oil the interface: this effect is observed both on the interface impedance and on the optical properties of the electrolyte. After this initial period, optical absorption measured during cycling a cell reveals a concentration evolution in the electrolyte in agreement with theoretical predictions. (c) 2005 Elsevier B.V. All rights reserved.