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A new sodium ferrous orthophosphate Na x Fe4(PO4)3 as anode materials for sodium-ion batteries

Zhang, Hui, Zhao, Yanming, Wen, Mingming, Dong, Youzhong, Fan, Qinghua, Kuang, Quan, Liu, Huatao, Lian, Xin
Journal of materials science 2018 v.53 no.11 pp. 8385-8397
anodes, batteries, dielectric spectroscopy, iron oxides, orthophosphates, sodium
A new sodium ferrous orthophosphate Na ₓ Fe₄(PO₄)₃ (1.1 ≤ x ≤ 1.2) with P2₁/n symmetry has been successfully synthesized via a solid-state reaction for the first time. The structure consists of FeO₅ pyramids, FeO₆ octahedron, and PO₄ tetrahedra which form large six-sided tunnels along [Formula: see text] direction and three- or four-sided tunnels running along [Formula: see text] direction. When evaluated as the anode materials for sodium-ion batteries, the first discharge and charge capacities of 553 and 264 mAh g⁻¹ for Na₁.₁Fe₄(PO₄)₃/C and 583 and 315 mAh g⁻¹ for Na₁.₂Fe₄(PO₄)₃/C, respectively, can be obtained at 10 mA g⁻¹ current density. Compared to the Na₁.₁Fe₄(PO₄)₃/C, Na₁.₂Fe₄(PO₄)₃/C exhibits a better cycling performance, where the charge capacity of about 100 mAh g⁻¹ can still be maintained after 15 cycles. The electrode kinetics are investigated further by the electrochemical impedance spectroscopy.