Identifying the Role of Electrolyte Additives for Lithium Plating on Graphite Electrode by Operando X‐ray Tomography

Abstract The plating of lithium metal on the graphite electrode is a major degradation mechanism in lithium‐ion batteries (LIBs). It brings a significant risk of internal shortcircuit by penetration of dendritic lithium through the separator, leading to short cycle life and safety issues. Understanding how and when plating occurs is crucial for the development of mitigation strategies, e. g. tuning the electrolyte composition. Here we present an operando X‐ray tomographic microscopy (XTM) study to directly monitor the plating of lithium metal in a lithium/graphite cell. XTM enables a non‐destructive and quantitative characterization at operando conditions of lithium deposition on a graphite electrode at relevant conditions. In this work it allows us to probe the role of the electrolyte additives vinylene carbonate (VC) and lithium bis(fluorosulfonyl)imide (LiFSI) in the standard LIB electrolyte LP57 (base electrolyte without additives). The additives show overall better performances in terms of delayed onset of lithium plating which is important for the utilisation of the full capacity of graphite intercallaiton. We show that there is a transition during lithiation of the dominating mechanism, once lithium plating is initiated this rapidly becomes dominating and hinders further intercalation. For the base electrolyte a homogeneous and dense morphology of plated lithium is found, whereas a more dendritic morphology is observed in the presence of additives. During delithiation, there is a rapid stripping of some of the plated lithium followed by deintercalation. In addition, our work provides a general methodology to track the morphology of plated lithium, which is crucial for fundamental research about battery safety.