MOF-derived Na3V2(PO4)3-carbon@graphene fibers for flexible fiber-shaped sodium ion battery

With the growing popularity of wearable devices, fiber-shaped rechargeable batteries become increasingly important as the next-generation energy storage devices. However, the practical applications are hindered by the limitation of sluggish kinetics of the Na⁺ transport and poor conductivity. Herein, a novel composite fiber was designed and fabricated as a cathode material for fiber-shaped Na-ion batteries (SIBs). The unique architecture on the fiber surface has three-dimensional porous structure, numerous channels for Na⁺ and electron transport, that facilitates electrolyte infiltration and strain-relaxed substructure. Na₃V₂(PO₄)₃ nanoparticles are uniformly incorporated into carbon matrix. The as-prepared fiber shows improved conductivity, accelerated Na⁺ diffusion kinetics and enhanced mechanical properties. The resulting composite fiber achieves a reversible specific capacity of 57.1mAh g⁻¹ after 1000 cycles with 86.0 % capacity retention and exhibited a superior rate capability via half-cells. Furthermore, the fiber-shaped full SIBs were also fabricated, which present a reversible capacity of 18.2 μAh cm⁻¹ at different bending angles. The full batteries exhibit excellent rate performance, stable cycling capability, and outstanding flexibility. This work may provide new insights into fiber-shaped SIBs for actual wearable applications.