Current-Density-Dependent Electroplating in Ca Electrolytes: From Globules to Dendrites

Multivalent cation rechargeable batteries, including those based on Ca, Mg, Al, etc., have attracted considerable interest as candidates for beyond Li-ion batteries. Recent developments have realized promising electrolyte compositions for rechargeable Ca batteries; however, an in-depth understanding of the Ca plating and stripping behavior and the mechanisms by which adverse dendritic growth may occur remains underdeveloped. In this work, via in situ transmission electron microscopy, we have captured the real-time nucleation, growth, and dissolution of Ca and the formation of dead Ca and demonstrated the critical role of current density and the solid-electrolyte interphase layer in controlling the plating morphology. In particular, the interface was found to influence Ca deposition morphology and can lead to Ca dendrite growth under unexpected conditions. These observations allow us to propose a model explaining the preferred conditions for reversible and efficient Ca plating.