Polyaniline-Coated Na₃V₂(PO₄)₂F₃ Cathode Enables Fast Sodium Ion Diffusion and Structural Stability in Rechargeable...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium-ion batteries (SIBs) are crucial for grid-scale energy storage.
• Sodium superionic conductor (NASICON) materials like Na3V2(PO4)2F3 (NVPF) show promise as SIB cathodes but suffer from poor electronic conductivity.
• Improving the electronic conductivity of NVPF is essential for high-performance SIBs.

Purpose of the Study:

• To develop a strategy for enhancing the electrochemical performance of NVPF.
• To synthesize and characterize a novel polyaniline (PANI)@NVPF composite material.
• To evaluate the suitability of PANI@NVPF as a cathode for high-rate sodium-ion battery applications.

Main Methods:

• A Pickering emulsion method was employed to create PANI@NVPF nanocomposites.
• X-ray diffraction (XRD) and Raman spectroscopy confirmed successful PANI coating without altering the NVPF structure.
• Thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) assessed thermal stability and morphology.
• Electrochemical performance was evaluated using sodium test cells, including rate capability and cycling stability.
• Ex-situ electron paramagnetic resonance (EPR) investigated the vanadium valence states during cycling.

Main Results:

• The PANI coating successfully enhanced interfacial bonding and electronic conductivity of NVPF.
• PANI@NVPF nanocomposites exhibited improved rate performance compared to pristine NVPF, with 2%PANI@NVPF retaining 70% capacity at 5C.
• Ex-situ EPR confirmed the presence of mixed V4+/V3+ valence states during electrochemical cycling.
• Sodium diffusion coefficients increased with cycling, reaching approximately 3.25 × 10^-11 cm^2 s^-1.
• The PANI coating improved sodium diffusion channels within the NVPF framework.

Conclusions:

• Polyaniline coating is an effective strategy to improve the electrochemical performance of NVPF for sodium-ion batteries.
• The PANI@NVPF nanocomposite demonstrates enhanced rate capability and improved sodium ion diffusion.
• These findings highlight PANI@NVPF as a promising cathode material for high-rate sodium-ion battery applications.