Effective Lithium Passivation through Graphite Coating for Lithium Metal Batteries

Metallic lithium reacts with organic solvents, resulting in their decomposition. The prevention of these decomposition reactions is a key aspect enabling the use of metallic lithium as an anode in lithium metal batteries. Scanning electrochemical microscopy (SECM), laser microscopy, and Fourier transform infrared (FT-IR) spectroscopy were used to analyze the effect of a graphite coating on metallic lithium. The graphite layer successfully prevents the agglomeration of decomposition products on the surface. SECM data show that the surface of untreated lithium metal in electrolyte is insulating, but the surface of the graphite coated lithium appears conducting and is therefore not covered by any layer of decomposition products. The protective properties of the graphite layer were proofed using FT-IR data. No significant differences in the spectra evolved during immersion of the sample in the electrolyte. Electrochemical plating experiments and post-mortem analysis revealed that the graphite layer did not result in homogeneous lithium plating depending on the current density. At high currents, no fully covering layer of decomposition products was formed on the surface during plating experiments, indicating a more complex mechanism of solid-electrolyte interface formation.