Hydridoborate‐based Solid‐state Electrolytes for Sodium Metal Batteries

Hydridoborates have emerged as promising candidates for solid‐state electrolytes in sodium metal batteries owing to their high ionic conductivity, thermal/electrochemical stability, good mechanical properties, and good compatible interface with electrodes. This review provides a comprehensive analysis of the recent advancements in the development and application of Na‐hydridoborate‐based solid‐state electrolytes. We explore the structural properties and electrochemical behaviors of various Na hydridoborates, including NaBH4, NaB3H8, closo‐borates, nido‐borates, etc. Additionally, we discuss the approaches for the synthesis of hydridoborate compounds with inexpensive raw chemicals and low toxicity. This review will inspire further efforts to develop fast Na‐ion conducting hydridoborate materials with favorable interfacial compatibility, promoting their applications in high‐performance all‐solid‐state sodium metal batteries.