A consideration of the morphology of electrochemically deposited lithium in an organic electrolyte

Lithium rechargeable cells with lithium metal anodes are widely considered to have the highest energy density among comparable cells. However the life cycle and thermal stability of these cells must be improved. The poor performance of lithium metal cells is mainly explained by lithium dendrite growth. With a view to overcoming this problem, we considered the lithium deposition mechanism. We have been carrying out various experiments on the lithium deposition behavior. In this paper we used these results to propose the current and most likely lithium deposition mechanism. We suggest that lithium dendrites may be called whiskers because their shape satisfies the definition of whiskers as `fibrous crystals'. Their tip morphology remains unchanged during their growth, which means they grow from the base in the same way as whiskers of tin from thin films under stress. Lithium deposited under a protective film will experience stress because the deposition is non-uniform. The protective film will break in order to release this stress thus, lithium whiskers may then grow in the form of extrusions. To support our assumption, we calculated the possible morphology of the lithium with the boundary condition that pressure induced by the surface tension is the same throughout the lithium surface. The calculation indicated three types of shape depending on the value of the surface tension and internal pressure. If lithium deformation is limited by the creep strength of bulk lithium and the lithium whiskers, the whisker growth is described by the calculated shape.