Sol-gel synthesis and electrochemical properties of fluorophosphates Na2Fe1−xMnxPO4F/C (x = 0, 0.1, 0.3, 0.7, 1) composite as cathode materials for lithium ion battery

• Published in: Journal of materials chemistry 2011-01, Vol.21 (46), p.1863-18637
• Main Authors: Wu, Xiaobiao, Zheng, Jianming, Gong, Zhengliang, Yang, Yong
• Format: Article
• Language: English
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/c1jm13578c

Fluorophosphates Na 2 Fe 1− x Mn x PO 4 F/C ( x = 0, 0.1, 0.3, 0.7, 1) composite were successfully synthesized via a sol-gel method. The structure, morphology and electrochemical performance of the as prepared materials were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and charge/discharge measurements. XRD results show that, consistent with Na 2 FePO 4 F, Na 2 Fe 0.9 Mn 0.1 PO 4 F ( x = 0.1) crystallize in a two-dimensional (2D) layered structure with space group Pbcn . However, increasing the content of Mn to x ≥ 0.3 results in a structure transition of Na 2 Fe 1− x Mn x PO 4 F from the 2D layered structure of Na 2 FePO 4 F to the three-dimensional (3D) tunnel structure of Na 2 MnPO 4 F. SEM and TEM analysis indicates nanostructured primary particles (about tens of nanometres in diameter) are obtained for all samples due to uniform carbon distribution and low calcining temperature used. Na 2 FePO 4 F is able to deliver a reversible capacity of up to 182 mA h g −1 (about 1.46 electrons exchanged per unit formula) with good cycling stability. Compared with Na 2 FePO 4 F, partial replacement of Fe by Mn in Na 2 Fe 1− x Mn x PO 4 F increases the discharge voltage plateau. Similar to Na 2 FePO 4 F, iron-manganese mixed solid solution Na 2 Fe 1− x Mn x PO 4 F ( x = 0.1, 0.3, 0.7) also show good cycling performance. Furthermore, Na 2 MnPO 4 F with high electrochemical activity was successfully prepared for the first time, which is able to deliver a discharge capacity of 98 mA h g −1 . The good electrochemical performance of Na 2 Fe 1− x Mn x PO 4 F materials can be attributed to the distinctive improvement of ionic/electronic conduction of the materials by formation of nanostructure composite with carbon. Nanostructured Na 2 Fe 1− x Mn x PO 4 F/C composites with good electrochemical performance are successfully synthesized by a novel sol-gel method. Na 2 MnPO 4 F exhibits reasonable electrochemical activity for the first time.