Spray-Drying Synthesis of Na₄Fe₃(PO4)₂P₂O₇@CNT Cathode for Ultra-Stable and High-Rate Sodium-Ion Batteries

Iron-based phosphate is a promising cathode for sodium-ion batteries due to its low cost and abundant resources; however, the practical application is hindered by poor electronic conductivity, sluggish Na⁺ diffusion, and a lack of low-cost and scalable synthesis methods. To address such issues, herein, we present a low-cost and scalable spray-drying strategy to synthesize Na₄Fe₃(PO₄)₂P₂O₇@CNT (NFPP@CNT) hollow microspheres. The NFPP@CNT composite has the following advantages: highly conductive CNT can significantly improve the electronic conductivity of the cathode, and the flexible CNT-based microsphere architecture facilitates Na⁺ diffusion and guarantees excellent mechanical properties to mitigate structural degradation during cycling. These merits make the NFPP@CNT cathode display outstanding electrochemical performances: the NFPP@CNT-1% electrode demonstrates a high reversible capacity of 103.9 mAh g^-1 at 0.1 C and maintains a very high capacity retention of 99.9% after 1000 cycles even at a high rate of 5 C.