Correlating the Formation Protocols of Solid Electrolyte Interphases with Practical Performance Metrics in Lithium Metal Batteries

The solid electrolyte interphase (SEI) is regarded as the most important and least understood component of lithium metal batteries (LMBs). Similarly, the connection between SEI formation protocols and the practical performance metrics in LMBs is even less understood. Here, we demonstrate the effects of constant current and constant voltage SEI formation protocols on Coulombic efficiency (CE) and corrosion losses in LMBs. The formation protocols produce SEIs that reduce parasitic lithium–electrolyte reactions, improving early cycle CE and mitigating corrosion of lithium metal. In addition, we establish that the thicker constant current SEIs formed at low current densities are better for passivating lithium than constant voltage SEIs, possibly due to reduced electrolyte permeability in the constant current SEIs. Using these SEI formation protocols in a high-performing electrolyte, we improve first-cycle CE by ∼5%, improve compounded CE in the first 5 cycles by ∼7%, and reduce corrosion-induced CE losses by ∼8%.