Introducing Symmetric Li-Ion Cells as a Tool to Study Cell Degradation Mechanisms

"Symmetric Li-ion cells" are assembled using two identical electrodes, one previously charged and one discharged. For example, a graphite/graphite symmetric cell is assembled using one lithiated graphite electrode and one graphite electrode, both of which have the same mass of graphite per unit area. Symmetric cells allow study of electrodes, electrolyte and electrolyte additives in only the limited potential range of the electrode contained in the symmetric cell, rather than in the presence of both a high potential positive electrode and a low potential negative electrode as in a full lithium ion cell. Graphite/graphite and lithium titanate/lithium titanate symmetric cells were studied and the results are reported with a major focus on the interpretation of the symmetric cell results. We conclude that symmetric cells are well-suited for fundamental studies of the impact of electrolyte additives and new electrode materials on cell degradation.