The importance of interphase contacts in Li ion electrodes: The meaning of the high-frequency impedance arc

Li insertion electrodes are made by pressing a mixture of active material and additives on a metallic substrate. Here we estimate how various interphase contacts affect the electrode kinetics. We apply variable external mechanical pressure onto different cathodes and measure their impedance response. Similar experiments are performed on dry composites in contact with: Al or Cu foil, or Ag paste. Most surprisingly, we find that the high-frequency impedance arc is due to the contact impedance between the metal and the electrode material. This is in fundamental contradiction with previous interpretations. We propose an equivalent circuit explaining the observed phenomena. (C) 2008 The Electrochemical Society.