Improving the Stability of Li Metal Anode/Solid Electrolyte Interfaces via an Li₃PO₄ Intermediate Layer: An Investigation of Surface Chemistry and Electronic Band Structure

Recently, researchers are extensively developing next-generation batteries, including all-solid-state batteries (ASSBs), to meet the increasing demand for electric vehicles (EVs) and renewable energy storage. Li metal has been considered an ideal anode material due to its high theoretical capacity and low redox potential. However, it is highly reactive and severe side reactions occur at the interface between Li metal anode and solid electrolytes (SEs), significantly affecting battery performance. Therefore, Li metal anodes have not yet been commercialized. To obtain a chemically stable Li metal anode, the authors examined the side reactions at the interface between the Li metal anode and oxide-type SE using surface analysis techniques such as time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and low-energy inverse photoelectron spectroscopy (LEIPS). In this paper, we present the results of interface analysis between Li metal anode/SE and discuss how to obtain a stable Li metal anode.