Sodium Ion Polyanionic Compounds

These sodium ion cathode materials feature a 3D framework of polyanion units (e.g., PO₄​, P₂​O₇​) which provides robust structural stability and safety, often at the cost of lower intrinsic electronic conductivity.

• Fluorophosphates:
  • NVPF: Na_3​V_2​(PO₄​)₂​F₃​ is a state-of-the-art polyanion cathode with a high operating potential (3.95 V) and high energy density.
  • Doped NVPF: Various doped versions exist to improve conductivity, including substitutions with Potassium (K), Magnesium (Mg), Aluminium (Al), Bismuth (Bi), Calcium (Ca), Chromium (Cr), Manganese (Mn), Titanium (Ti), and Tungsten (W).
• Phosphates and Pyrophosphates:
  • NASICON: The prototypical Na_3​V₂​(PO₄​)₃​.
  • NFPP: Na₄​Fe₃​(PO_4​)_2​P_2​O₇​ is an iron-based alternative that eliminates expensive vanadium. It offers exceptional cycle life (>6,000 cycles) and thermal stability, making it ideal for grid storage.
  • NVP: Na_3​V₂​(PO_4​)_3​.

References

1. Liang, Y., Xu, L., & Sun, Z. (2025). Recent research progress in the application of Na3V2(PO4)2F3 cathode materials in sodium-ion batteries: synthesis, modification, and battery optimization. Energy Materials, 5, 500115.

See also

Sodium Ion Cathodes, Layered Transition Metal Oxides, Prussian Blue Analogues, Organic Cathode Materials