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/cm 2 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.