Cyclic electrochemical reactions on a Li-metal negative electrode having a low-resistance interface with a solid-state electrolyte

Li metal is a promising negative-electrode material for high-energy-density all-solid-state batteries. However, the surface of Li metal is prone to oxidation, which results in the formation of a contamination layer at the Li metal–solid electrolyte interface. This interfacial contamination layer is the root cause of short-circuiting and poor cycle stability, thus hindering the development of all-solid-state batteries. Prior studies have not quantitatively assessed the effect of the above layer on battery performance. Herein, the degradation mechanisms affecting the interface are investigated using alternating-current impedance measurements and Li plating–stripping cycle tests for a symmetric cell. A thin contamination layer results in a Li–electrolyte interface with a low resistance of 0.20 kΩ cm² and stable Li plating–stripping behavior at a current density of 3 mA cm⁻², whereas a thick contamination layer results in a high interfacial resistance of 2.0 kΩ cm². The thinning of the contamination layer on Li metal enhances the stability of the Li–electrolyte interface and Li plating–stripping kinetics.