Room-Temperature Synthesis of Carbon-Encapsulated Na3V2O2(PO4)2F Nanoparticles: A Cost-Effective, High-Power Cathode for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) offer a propitious choice to lithium-ion batteries (LIBs) due to sodium’s abundance and lower cost. However, SIBs’ commercial adoption is hindered by their lower energy density and higher cathode material production costs compared to those of LIBs. This study synthesizes Na₃V₂O₂(PO₄)₂F (NVOPF) nanoparticles at room temperature using solid-state mechanochemical synthesis, followed by carbon encapsulation. Pristine NVOPF achieves an initial gravimetric discharge capacity of 100 mAh g^–1 at a 0.1 C rate and delivers 98 mAh g^–1 at a 1 C rate, retaining 80% of its capacity over 250 cycles at a 1 C rate. Incorporating high surface area carbon (HSAC) enhances the intrinsic electronic conductivity of NVOPF. The HSAC-NVOPF composite shows improved cycling stability and higher rate capability, retaining 89.9% of its initial capacity after 500 cycles at a 1 C rate and 90% after 1000 cycles at 3 C rate due to fast sodium-ion diffusion and delivering 94 mAh g^–1 at a 20 C rate. This improvement is attributed to enhanced electrochemical reversibility and Na⁺-ion reaction kinetics. Reduced voltage–polarization values (113 and 111 mV for the composite vs 162 mV and 160 mV for pristine NVOPF) and lower charge transfer resistance (113 Ω cm² compared to 224 Ω cm²) indicate improved Na⁺ ion diffusion, highlighting the potential of NVOPF cathode for promising SIBs.