AlF3 Mediated In-Situ Cathode Interface Stabilization Enables High-Rate and Long-Life Na-Ion Batteries at Elevated Temperature

The instability of the cathode electrolyte interface (CEI) under high voltage and elevated temperature poses a major challenge to the practical application of Na 3 V 2 (PO 4 ) 2 O 2 F (NVOPF) cathodes in sodium-ion batteries (SIBs). To overcome this issue, we introduce a dual-functional AlF 3 coating that effectively stabilizes the interface while improving bulk electronic conductivity. The AlF 3 -modified NVOPF@C exhibits exceptional cycling stability at 55°C, maintaining 84.9% capacity after 1000 cycles at 10 C in half cells and 96.8% at 5 C in full cells using hard carbon anodes. Detailed characterization reveals that the AlF 3 coating promotes the formation of a robust, inorganic-rich CEI, primarily composed of a NaF/AlF 3 /NaAlF 4 ternary fluoride composite. This newly constructed CEI layer not only acts as a protective barrier to suppress detrimental interfacial side reactions but also serves as an efficient ionic conductor to facilitate Na + diffusion. In addition, the AlF 3 coating induces the creation of F─Al─O bridging bonds with surface oxygen groups, which collaborate with carbon nanotubes to establish a highly continuous conductive network that enables efficient electron transfer. These findings underscore the crucial significance of constructing a stable inorganic-dominated CEI and continuous conductive pathways for developing high-rate and thermally stable SIBs.