Cover Image, Volume 4, Issue 4, July 2025

Front Cover: Solid-state electrolytes are essential for developing safe and efficient lithium metal batteries. In article number BTE.70007, Xinhao Yang and co-workers investigate the effect of AlF₃ incorporation on lithium borate glass electrolytes, revealing a counterintuitive performance deterioration. While fluoride additives are widely used to enhance interfacial stability, their incorporation into the glass matrix was found to reduce ionic conductivity and lead to early short-circuiting under moderate current densities. In contrast, fluoride-free lithium borate glasses exhibited excellent thermal stability, wide electrochemical windows, and maintained stable operation for 500 hours under current densities ranging from 0.04 to 1 mA cm^-2. This work provides critical insights into the complex interplay between fluoride content, glass chemistry, and electrochemical performance, offering new guidelines for interfacial design in solid-state batteries.