Electrospun NaMnPO4–carbon nanofiber composite: a novel freestanding cathode for Na-ion batteries

Flexible, binder-free electrodes are increasingly attractive for next-generation sodium-ion batteries, where lightweight architectures and simplified processing can increase energy density and reduce costs. Here, we present a freestanding NaMnPO4–carbon nanofiber (NaMnPO4–CNF) cathode obtained through a single-step electrospinning process that simultaneously forms the active phase and the electrode, eliminating binders, conductive additives and metallic current collectors. Structural analyses reveal a mixed maricite–olivine NaMnPO4 phase uniformly embedded within a conductive N-doped CNF network. The resulting fibrous architecture exhibits hierarchical porosity and a high surface area (119 m2 g− 1 ), which promote electrolyte infiltration and fast Na+ transport. When tested in Na-ion half-cells, the NaMnPO4–CNF electrode delivers ~143 mAh g− 1 at 0.1C (92% of the theoretical capacity) and retains ~135, ~110 and ~ 90 mAh g− 1 at 0.5C, 1C and 2C, respectively, with Coulombic efficiencies above 95%. Long-term cycling confirms excellent durability, with ~140 mAh g− 1 at 0.1C, ~125 mAh g− 1 at 0.5C and ~ 80 mAh g− 1 at 2C after 500 cycles. Post-mortem analyses show that, despite progressive amorphization of the NaMnPO4 phase, the CNF matrix preserves structural integrity and elemental homogeneity. Compared with previously reported maricite NaMnPO4 cathodes, the freestanding NaMnPO4–CNF electrode offers markedly improved capacity, rate performance and cycling stability across a broader current range. This work demonstrates, for the first time, a dual-phase NaMnPO4 cathode integrated into an electrospun, binder-free architecture with state-of-the-art performance, opening a promising route toward flexible, energy-dense and low-cost sodium-ion batteries.