Electrochemical performance of mixed valence Na3V2O2x(PO4)2F3−2x/C as cathode for sodium-ion batteries

• Published in: Journal of power sources Vol. 241; pp. 56 - 60
• Main Authors: Serras, Paula, Palomares, Verónica, Goñi, Aintzane, Kubiak, Pierre, Rojo, Teófilo
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2013; Elsevier
• Subjects: Applied sciences; Carbon; Cycles; Direct energy conversion and energy accumulation; Electric potential; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical analysis; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrochemistry; Exact sciences and technology; Insertion; Low carbon steels; Materials; Mixed-valence; Na-ion batteries; Sodium; Sodium vanadium fluorophosphates; Surface layer; Texture; Mixed-valence; Electrochemistry; Sodium vanadium fluorophosphates; Na-ion batteries; Phosphates; Vanadium Fluophosphates; Sodium-ion battery; Cathode; Secondary cell; Electrode material; Phosphorus Compounds; Electrochemical characteristic; Inorganic anion; Sodium; Mixed valence; Electrical characteristic
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2013.04.094

A composite made of a mixed-valence sodium–vanadium fluorophosphate and 6.4% wt. carbon, Na3V2O2x(PO4)2F3−2x/C (0 < x < 1), has been prepared. Structural and magnetic characterization confirmed the +3/+4 oxidation state of vanadium in the phase. Morphological and texture analyses showed that carbon forms a network surrounding the particles, leading to a mesoporous composite with a high specific area of 67 m2 g−1. Electrochemical characterization conducted in Swagelok cells by cyclic voltammetry and galvanostatic cycling indicated that sodium extraction/insertion proceeds through a complex mechanism in two voltage pseudo-plateaux at 3.6 and 4.1 V vs. Na/Na+. Rate capability of the material ranges from specific capacities of 100 mAh g−1 at C/20 to 75 mAh g−1 at 5C. Cycling stability at 1C showed coulombic efficiency higher than 99% and capacity retention of 95% after 200 cycles. •Simple synthesis of mixed valence Na3V2O2x(PO4)2F3−2x/C composite (0 < x < 1).•Composite electrodes operate at 3.6–4.1 V vs. Na/Na+ with high specific capacity (100 mAh g−1 at C/20).•Composite electrodes show excellent rate capability for charging rates up to 5C (75 mAh g−1).•Superior reversibility and stability are observed for 200 cycles at 1C (95 mAh g−1).