Abstract
A new alluaudite-type Na2VFe2(PO4)3 with carbon composite has been prepared for the first time via a simple sol-gel method using citric acid as an assistant agent and carbon source. The crystal structure and morphology of Na2VFe2(PO4)3/C composite are well characterized by X-ray diffraction, scan electron microscope, and energy-dispersive X-ray analysis. The experimental results show that a three-dimensional [VFe2(PO3)3]2− framework in this alluaudite structure provides two types of tunnels to enable the sodium-ion transporting which contributes to the electrochemical performance. When evaluated as a cathode for sodium-ion batteries, Na2VFe2(PO4)3/C composite delivers the first specific charge capacity of 66.7 mAh g−1 and discharge capacity of 65.8 mAh g−1 at 5 mA g−1 current density. After 100 cycles, the charge capacity (~52.2 mAh g−1at 5 mA g−1) shows a good capacity retention (~78%) compared to the first cycle. Cyclic voltammetric profiles confirm the activated multi-electron reactions including the Fe2+/Fe3+, V2+/V3+, and V3+/V4+ redox couples. Furthermore, the diffusion coefficient of sodium-ion (D Na +) in this structure is also calculated based on the result of electrochemical impedance spectroscopy.
Published Version
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