Enabling the Electrochemical Activity in Sodium Iron Metaphosphate [NaFe(PO3)3] Sodium Battery Insertion Material: Structural and Electrochemical Insights

• Published in: Inorganic chemistry Vol. 56; no. 10; pp. 5918 - 5929
• Main Authors: Gond, Ritambhara, Meena, Sher Singh, Yusuf, S. M, Shukla, Vivekanand, Jena, Naresh K, Ahuja, Rajeev, Okada, Shigeto, Barpanda, Prabeer
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.05.2017
• ISSN: 0020-1669; 1520-510X; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b00561

Sodium-ion batteries are widely pursued as an economic alternative to lithium-ion battery technology, where Fe- and Mn-based compounds are particularly attractive owing to their elemental abundance. Pursuing phosphate-based polyanionic chemistry, recently solid-state prepared NaFe­(PO3)3 metaphosphate was unveiled as a novel potential sodium insertion material, although it was found to be electrochemically inactive. In the current work, employing energy-savvy solution combustion synthesis, NaFe2+(PO3)3 was produced from low-cost Fe3+ precursors. Owing to the formation of nanoscale carbon-coated product, electrochemical activity was enabled in NaFe­(PO3)3 for the first time. In congruence with the first principles density functional theory (DFT) calculations, an Fe3+/Fe2+ redox activity centered at 2.8 V (vs Na/Na+) was observed. Further, the solid-solution metaphosphate family Na­(Fe1–x Mn x )­(PO3)3 (x = 0–1) was prepared for the first time. Their structure and distribution of transition metals (TM = Fe/Mn) was analyzed with synchrotron diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy. Synergizing experimental and computational tools, NaFe­(PO3)3 metaphosphate is presented as an electrochemically active sodium insertion host material.