Architecting Na₃V₂(PO₄)₃ microflower cathodes with NaF-rich interfaces for ultrafast and ultrastable sodium-ion storage

Na₃V₂(PO₄)₃ with a NASICON framework stands out as a compelling cathode for sodium-ion batteries (SIBs) due to its open Na⁺ transport channels and stable crystal framework. However, its fast-charging capability remains constrained by the poor electrical conductivity and uncontrolled growth of cathode-electrolyte interfacial layers under high rates. Herein, carbon dots (CDs) are employed to couple bulk architectural engineering with interfacial chemistry reconstruction in Na₃V₂(PO₄)₃, enabling the rapid ion/electron transport. First, the CDs can guide the self-assembly of two-dimensional nanosheet subunits into hierarchical nanoflower-like microspheres, thereby shortening Na⁺ diffusion pathways. Second, the introduced CDs generate a thin carbon layer that effectively improves electrical conductivity with a limited carbon content. Third, the CDs-regulated surface chemistry promotes the formation of a thin, uniform, and NaF-rich CEI layer, which accelerates interfacial charge transfer. Consequently, the optimized cathode delivers 108.8 mAh g^-1 at 1 C and 49.5 mAh g^-1 at 300 C, while maintaining 95.5% capacity retention after 50000 cycles. Moreover, the corresponding full cell achieves a high energy density of 382.6 Wh kg^-1 and retains 226.2 Wh kg^-1 within a short charging time of approximately 102.2 s. Overall, these results highlight CDs-mediated structural and interfacial regulation as an effective route toward fast-charging SIBs.