Synergistic effect of carbon and MnO2 coated Na3V2(PO4)2F3 cathode for high-performance sodium-ion batteries

Sodium-ion batteries (SIBs) are considered a promising alternative to lithium-ion batteries (LIBs) due to their abundant resources and low cost. However, the relatively large radius and mass of sodium ions can lead to structural degradation and volume changes in the electrode materials during charging and discharging processes, which limits their practical applications. In this paper, we successfully prepared carbon and MnO 2 co-coated Na 3 V 2 (PO 4 ) 2 F 3 (NVPF/C@ M-x, x = 0, 1, 3, 5 wt%) cathode materials using sol-gel method and suspension coating method. We systematically studied the physical and chemical effects of the MnO 2 coating, as well as the electrochemical performance of the materials. The results demonstrate that an optimal MnO₂ coating (1 wt%) forms a uniform interfacial layer, which not only suppresses Na + dissolution and side reactions but also enhances electronic conductivity and structural stability. NVPF/C@M-1 exhibits a reversible specific capacity of 129.09 mAh g −1 at 0.1C and maintains a capacity of 59.44 mAh g −1 at 10C. Furthermore, after 300 cycles at 1C and 500 cycles at 5C, the capacity retention rates are 85.96% and 89.34%, respectively. Kinetic analysis reveals that the MnO 2 coating significantly reduces the charge transfer resistance (R ct ) and increases the sodium ion diffusion coefficient (D Na+ ), thereby optimizing the rate performance and cycling stability of the materials. Additionally, the MnO 2 and C co-coating structure significantly improves the low-temperature performance, with the NVPF/C@M-1 electrode maintaining 90.43% capacity retention even at −30 °C, far superior to the uncoated sample's 64.13%. The NVPF/C@M-1 cathode demonstrates significantly enhanced overall performance in sodium-ion full-cell tests. It delivers an initial discharge capacity of 107.78 mAh g −1 at 1C, maintains a capacity retention rate of 95.07% after 100 cycles, and retains a discharge capacity of 81.63 mAh g −1 even at the high rate of 5C. This study provides an effective strategy for developing high-performance cathode materials for sodium-ion batteries. • A uniform MnO 2 and carbon co-coating layer was constructed on Na 3 V 2 (PO 4 ) 2 F 3 via a scalable suspension method, which effectively enhances interfacial stability and electronic conductivity while suppressing vanadium dissolution and side reactions. • The optimized NVPF/C@M-1 cathode delivers exceptional electrochemical performance, including a high reversible capacity (129.09 mAh g -1 at 0.1 C), remarkable rate capability (59.44 mAh g -1 at 10 C), and outstanding cycling stability (89.34% retention after 500 cycles at 5 C). • Superior low-temperature performance is achieved with 90.43% capacity retention at -30 °C, supported by improved Na + diffusion kinetics and reduced charge transfer resistance as verified through systematic kinetic analyses.