Interphase design enabling stable cycling of all-solid-state lithium metal batteries by in-situ X-ray photoelectron spectroscopy lithium metal sputtering

Interface compatibility is one of the key issues for all-solid-state lithium metal batteries (ASSLMBs). The interface problems include the formation of lithiophobic phases (e.g., Li2CO3) on the surface of the solid electrolytes to worsen the solid-solid interface contact and the continuous parasitic reactions between the highly reactive lithium metal and the electrolyte during cycling. In this work, the in-situ XPS (X-ray Photoelectron Spectroscopy) characterization is used to study the interface between lithium metal and Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte using different modification strategies. An ultra-thin composite modification layer of 6 nm Au-6 nm LiF is deposited on the LAGP, which is called C-LAGP. The Li|C-LAGP|Li symmetric cell can be stably cycled for more than 800 h at room temperature at the current density of 0.1 mA cm−2, and the critical current density can reach 1 mA cm−2. The LiFePO4|C-LAGP|Li solid-state battery delivers good cycling stability and high reversible capacity at room temperature. All these good electrochemical performances are resulted from the well-constructed interfacial structure at the solid electrolyte/Li contact. This work provides new ideas and characterization methods for the design of artificial modification layers to solve the interface issues for all-solid-state lithium metal batteries.