Ionothermal Synthesis of High-Voltage Alluaudite Na2+2xFe2-x(SO4)3 Sodium Insertion Compound: Structural, Electronic, and Magnetic Insights

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• 作者：Debasmita Dwibedi ; Chris D. Ling ; Rafael B. Araujo ; Sudip Chakraborty ; Shanmughasundaram Duraisamy ; Nookala Munichandraiah ; Rajeev Ahuja ; Prabeer Barpanda
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：March 23, 2016
• 年：2016
• 卷：8
• 期：11
• 页码：6982-6991
• 全文大小：665K
• ISSN：1944-8252

文摘

Exploring future cathode materials for sodium-ion batteries, alluaudite class of Na₂Fe^II₂(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 Na_2+2xFe^II_2-x(SO₄)₃. It marks the first demonstration of solvothermal synthesis of alluaudite Na_2+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 Na_2+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.