Carbon Nanofiber/Na₃V₂(PO₄)₂F₃ Particle Composites as a Self-Standing Cathode for High-Voltage Flexible Sodium-Ion Batteries

Smart wearable electronic devices are becoming more prevalent in our daily life, exceedingly arousing the increasing demand for flexible energy storage devices. Herein, a sodium superionic conductor (NASICON)-structured Na₃V₂(PO₄)₂F₃ (NVPF) self-standing cathode is fabricated via an electrospinning technique. NVPF particles at the nanoscale are encapsulated in or attached to the surface of carbon nanofibers to form an NVPF self-standing cathode, which exhibits a high-voltage platform of ∼4.07 V with a reversible capacity of 101.8 mAh g^–1 at 0.2C and 98.3% capacity retention after 400 cycles. Moreover, the soft package full battery, assembled with an NVPF self-standing cathode and a Na₃V₂(PO₄)₃ (NVP) anode, can light up a light-emitting diode in the folded/unfolded states. The superior sodium storage performance was enabled by the stable structure of the NVPF self-standing cathode. Moreover, the nitrogen-doped carbon nanofiber network of the NVPF self-standing cathode not only ensures the flexibility but also facilitates electron and Na⁺ transportation. This work provides an NVPF self-standing cathode with excellent mechanical and electrochemical performance for high-voltage flexible sodium-ion batteries, which is beneficial for promoting the practical application of high-voltage flexible sodium-ion batteries.