title: Ionothermal Synthesis of High-Voltage Alluaudite Na2+2xFe2-x(SO4)3 Sodium Insertion Compound: Structural, Electronic, and Magnetic Insights.
abstract: Exploring future cathode materials for sodium-ion batteries, alluaudite class of Na2Fe(II)2(SO4)3 has been recently unveiled as a 3.8 V positive insertion candidate (Barpanda et al. Nat. Commun. 2014, 5, 4358). It forms an Fe-based polyanionic compound delivering the highest Fe-redox potential along with excellent rate kinetics and reversibility. However, like all known SO4-based insertion materials, its synthesis is cumbersome that warrants careful processing avoiding any aqueous exposure. Here, an alternate low temperature ionothermal synthesis has been described to produce the alluaudite Na2+2xFe(II)2-x(SO4)3. It marks the first demonstration of solvothermal synthesis of alluaudite Na2+2xM(II)2-x(SO4)3 (M = 3d metals) family of cathodes. Unlike classical solid-state route, this solvothermal route favors sustainable synthesis of homogeneous nanostructured alluaudite products at only 300 °C, the lowest temperature value until date. The current work reports the synthetic aspects of pristine and modified ionothermal synthesis of Na2+2xFe(II)2-x(SO4)3 having tunable size (300 nm ∼5 μm) and morphology. It shows antiferromagnetic ordering below 12 K. A reversible capacity in excess of 80 mAh/g was obtained with good rate kinetics and cycling stability over 50 cycles. Using a synergistic approach combining experimental and ab initio DFT analysis, the structural, magnetic, electronic, and electrochemical properties and the structural limitation to extract full capacity have been described.
authors.affiliation: Faraday Materials Laboratory, Materials Research Center, Indian Institute of Science , C.V. Raman Avenue, Bangalore 560012, India.
authors.forename: Debasmita
authors.initials: D
authors.lastname: Dwibedi
authors.affiliation: School of Chemistry, The University of Sydney , Building F11, Sydney, NSW 2006, Australia.
authors.forename: Chris D
authors.initials: CD
authors.lastname: Ling
authors.affiliation: Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University , Box 516, 75120 Uppsala, Sweden.
authors.forename: Rafael B
authors.initials: RB
authors.lastname: Araujo
authors.affiliation: Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University , Box 516, 75120 Uppsala, Sweden.
authors.forename: Sudip
authors.initials: S
authors.lastname: Chakraborty
authors.affiliation: Inorganic and Physical Chemistry, Indian Institute of Science , C.V. Raman Avenue, Bangalore, 560012, India.
authors.forename: Shanmughasundaram
authors.initials: S
authors.lastname: Duraisamy
authors.affiliation: Inorganic and Physical Chemistry, Indian Institute of Science , C.V. Raman Avenue, Bangalore, 560012, India.
authors.forename: Nookala
authors.initials: N
authors.lastname: Munichandraiah
authors.affiliation: Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University , Box 516, 75120 Uppsala, Sweden.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Ahuja
authors.affiliation: Faraday Materials Laboratory, Materials Research Center, Indian Institute of Science , C.V. Raman Avenue, Bangalore 560012, India.
authors.forename: Prabeer
authors.initials: P
authors.lastname: Barpanda
keywords: DFT; Na2Fe2(SO4)3; alluaudite; ionothermal synthesis; sodium-ion battery