The degradation of the lithium (Li) electrode was investigated based on its structural transformation due to the inactivation of deposited Li using a Copper/LiNi1/3Mn1/3Co1/3O2 (NMC) cell and a Li vertical bar Li symmetrical cell. Depletion of active Li turned out to be the major reason for the failure of the Li electrode under our experimental conditions. Following the first charging (Li-deposition) of the Copper/NMC cell, the discharge process only recovered 23% of the total deposited Li back to the NMC cathode. Electrochemical impedance spectroscopy (EIS) experiments of the Li vertical bar Li symmetric cell demonstrated that the repeated inactivation during the deposition process leads to the growth of the deposited Li layer thereby forming three interfacial structures most likely originating from (i) residual Li vertical bar liquid electrolyte, (ii) cycled Li in the inner deposited Li layer vertical bar liquid electrolyte, and (iii) cycled Li on the outer deposited Li layer vertical bar liquid electrolyte. The voltage profile and EIS of the symmetric cell could be correlated with the degradation behavior exhibited by the Li electrode. (C) 2014 The Electrochemical Society. All rights reserved.