Advances and prospects of key technologies for sodium-salt solid-state energy storage batteries: A focus on practical β″-Al2O3 electrolyte-based batteries and their industrial breakthroughs

Sodium-salt solid-state energy storage batteries (SSSEBs) have attracted extensive attention owing to their high safety and low cost. This review argues that among the various SSSEB technological routes, the sodium‑nickel chloride battery employing β″-Al 2 O 3 as the solid electrolyte, metallic sodium as the anode, and NaCl/Ni as the cathode represents the one of the most mature solid-state battery technology that has achieved large-scale field deployment. To date, over 5.5 million cells have been sold, the installed capacity exceeds 500 MWh, the system has passed all safety tests of the United States Advanced Battery Consortium, exhibits a cycle life exceeding 4500 cycles, and enables 100% material recycling. The practical cell-level energy density is 100–120 Wh kg −1 , with a theoretical potential exceeding 500 Wh kg −1 at the active material level. This review systematically summarizes the core components of SSSEBs (solid electrolytes and electrode materials) and ion transport mechanisms, highlights the structural advantages, engineering progress, and industrial application examples of β″-Al 2 O 3 -based SSSEBs, and thoroughly analyzes three major technical challenges: interface compatibility, sodium dendrite growth, and scalable fabrication. Major safety hazards and thermal runaway protection measures are also critically evaluated. Finally, based on real project data, future development directions and key breakthrough points are envisioned, aiming to provide researchers with a comprehensive technical reference that balances academic frontiers and industrial implementation.