A Family of High-Performance Cathode Materials for Na-ion Batteries, Na3(VO1−xPO4)2 F1+2x (0 ≤ x ≤ 1): Combined First-Principles and Experimental Study

• Published in: Advanced functional materials Vol. 24; no. 29; pp. 4603 - 4614
• Main Authors: Park, Young-Uk, Seo, Dong-Hwa, Kim, Hyungsub, Kim, Jongsoon, Lee, Seongsu, Kim, Byoungkook, Kang, Kisuk
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 06.08.2014
• Subjects: cathode materials; first-principle calculations; fluorophosphates; Na-ion batteries; sodium
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201400561

Room‐temperature Na‐ion batteries (NIBs) have recently attracted attention as potential alternatives to current Li‐ion batteries (LIBs). The natural abundance of sodium and the similarity between the electrochemical properties of NIBs and LIBs make NIBs well suited for applications requiring low cost and long‐term reliability. Here, the first successful synthesis of a series of Na3(VO1−x PO4)2F1+2x (0 ≤ x ≤ 1) compounds as a new family of high‐performance cathode materials for NIBs is reported. The Na3(VO1−x PO4)2F1+2x series can function as high‐performance cathodes for NIBs with high energy density and good cycle life, although the redox mechanism varies depending on the composition. The combined first‐principles calculations and experimental analysis reveal the detailed structural and electrochemical mechanisms of the various compositions in solid solutions of Na3(VOPO4)2F and Na3V2(PO4)2F3. The comparative data for the Na y (VO1−x PO4)2F1+2x electrodes show a clear relationship among V3+/V4+/V5+ redox reactions, Na+−Na+ interactions, and Na+ intercalation mechanisms in NIBs. The new family of high‐energy cathode materials reported here is expected to spur the development of low‐cost, high‐performance NIBs. A full solid solution of Na3(VO1−x PO4)2F1+2x (0 ≤ x ≤ 1) compounds as a promising cathode group for Na‐ion batteries is introduced. A systematic study using a combined theoretical and experimental approach explains the electrochemical properties of the Na y (VO1−x PO4)2F1+2x electrodes and reveals their reaction mechanism in terms of V3+/V4+/V5+ redox reactions, the effect of fluorine, and Na+−Na+ interactions.