Ultrafast deposition of faceted lithium polyhedra by outpacing SEI formation

Abstract Electrodeposition of lithium metal is critical for high energy batteries. However, the simultaneous formation of a surface corrosion film termed the solid electrolyte interphase (SEI) complicates the deposition process. Here, we decouple these two intertwined processes by outpacing corrosion at ultrafast deposition current densities while also avoiding mass transport limitations. Using cryogenic-electron microscopy, we discover the intrinsic deposition morphology of metallic lithium to be that of a rhombic dodecahedron, which is surprisingly independent of electrolyte chemistry or current collector substrate. In a coin cell architecture, these rhombic dodecahedra reveal a key failure mode at high current densities: rather than promoting dendritic morphologies, the near point-contact electrical connectivity of the polyhedra to the current collector accelerates inactive Li formation that can explain poor cycling efficiency at high current densities. While Li deposition and SEI formation have always been tightly linked in past studies, our experimental approach enables new opportunities to fundamentally understand these processes decoupled from each other and bring about new insights to engineer better batteries.