Multifunctional Mg–C Bilayer Interphase for Anode-Free Solid-State Batteries

The development of anode-free solid-state batteries can significantly improve the energy density of today's lithium-ion batteries, but it has proven difficult due to challenges in regulating Li deposition/dissolution. Here, we report a Mg/C bilayer interphase for anode-free batteries. We observed the lithiation of both Mg and C prior to the initial plating process. Moreover, a larger nucleation overpotential can be observed on lithiated carbon (Li-C) than on lithiated magnesium (Li-Mg). As a result, instead of plating at the interface between Li-C and the solid electrolyte (SE), Li will penetrate through the Li-C and the plate at the interface between Li-C and Li-Mg. The regulated Li plating was also validated through cross-sectional scanning electron microscopy images. As a result, a uniform Li plating and stripping can be achieved underneath the Li-C. The effective separation of the SE and the plated Li enabled stable plating/stripping cycles at an areal capacity of 2 mAh/cm² at room temperature with an average Coulombic efficiency of >99%. The results provide important insights into understanding and designing interlayers for anode-free solid-state batteries.