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 interface compatible 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, to promote their applications in high-performance all-solid-state sodium metal batteries.