Novel acetic acid induced Na-rich Prussian blue nanocubes with iron defects as cathodes for sodium ion batteries

• Main Authors: Li, Lan, Nie, Ping, Chen, Yubo, Wang, Jie
• Other Authors: School of Materials Science and Engineering
• Format: Article
• Language: English
• Published: 2021
• Subjects: Engineering::Materials; Acetic Acid; Cathodes
• Online Access: https://hdl.handle.net/10356/151630
• Institution: Nanyang Technological University

The Prussian blue cathode has great potential for use in sodium-ion batteries in view of its high gravimetric capacity, facile synthetic procedure and low cost. The main challenges for Prussian blue are the structural degradation caused by [Fe(CN)₆] vacancies and coordinated water in its lattice and low average voltage due to insufficient activation of low-spin FeLS(C) redox-couple reactions. Here, Na-enriched Prussian blue with low coordinated water and free [Fe(CN)₆] vacancies has been successfully synthesized by defect engineering, using acetic acid as an iron defect inducer. In particular, Na-rich Na₃.₂₇Fe₀.₃₅[Fe(CN)₆]·0.85H₂O nanocubes with hole centres, low amounts of coordinated water and free [Fe(CN)₆] vacancies exhibit a high specific capacity, impressive cycling stability and good coulombic efficiency. This Na-rich material shows a low charge-transfer resistance (201.1 Ω), a high Na+ apparent diffusion coefficient (3.56 × 10⁻¹¹cm²s⁻¹) and an additional capacity contribution at approximately 4.1 V, demonstrating the sufficient activation of low-spin FeLS(C) redox couples in Na-involved reactions. The Na₃.₂₇Fe₀.₃₅[Fe(CN)₆]·0.85H₂O cathode undergoes a reversible redox reaction, which converts the structure from cubic Na₂Fe₀.₃₅[Fe(CN)₆] to rhombohedral Na₃.₂₄Fe₀.₃₅[Fe(CN)₆]. More significantly, this work for the first time realizes the rational composition and architecture design of Prussian blue materials by defect engineering for a broad range of potential applications.