With a theoretical specific capacity of 3862 mAh/g and other desirable properties such as high voltage, light weight, and high energy density, metallic lithium remains one of the materials of greatest promise for advanced battery applications. However, the complicated reactivity of this electrode with most practical battery electrolytes leads to substantial morphological and chemical changes that affect the safety and efficiency of the system, and have prevented its further implementation on rechargeable batteries. In this work we demonstrate how to establish a direct and systematic relationship between such morphological changes in the lithium electrode and the cycle performance of the battery. We demonstrate that the main morphological changes are associated with the decomposition of the redox-formed SEI layer, which follows different electrochemical pathways leading to different morphologies depending on the cycling rate of the cell. At high cycling rates (i > 0.16 mAcm(-2)), a three-layer morphology (dendritic layer, porous layer, residual lithium layer) is observed. At low cycling rates (i <= 0.16 mAcm(-2)), polymerization of electrolyte's solvents and gas evolution leading to macroscopic bubble clusters is observed. Furthermore, we demonstrate the advantages of using these systematic morphology-property relationships to fit and interpret complicated electrochemical impedance spectroscopy (EIS) data. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.100206jes] All rights reserved.