Morphological Transitions on Lithium Metal Anodes

Coin cells were prepared using a metallic lithium anode, a Li(4)Ti(5)O(12) cathode, and a 1.2 M LiPF(6)/ethylene carbonate:ethyl methyl carbonate (30:70 wt %) electrolyte. The cells were cycled galvanostatically between 1 and 2 V vs Li/Li(+) (i=2.0 mA/cm(2)) at a 2C rate. After a specific number of cycles, the cells were disassembled and the morphology of the lithium anode was characterized using scanning electron microscopy. It was observed that the surface morphology of the lithium metal electrode transitioned from a flat and smooth morphology to a microscopically rugged structure that shows three distinct layers: a top dendritic layer, an intermediate porous layer, and a residual metallic lithium layer. Morphological and electrochemical evidence points to the depletion of the electrolyte and the active metallic lithium that reacted to produce the porous layer as the most likely cause of cell failure under the conditions studied.