Effect of magnetic treatment on microstructure and cycle performance of LiFePO4/C cathode material
Introduction
Currently, an extensive study has been made on the LiFePO4 composite due to its inexpensive cost and environmentally friendly to humanity [1], [2], [3]. However, the poor cycle stability hinders its commercial applications. Pang et al [4] reported that the LiFePO4 composite prepared by a solid-phase method only has a capacity retention of 93% at 30 charge–discharge cycles. Zhao et al [5] utilized the solvothermal method and prepared LiFePO4/graphene and LiFePO4/carbon-nanotube composite, and the capacity retentions at 100 charge–discharge cycles are 96% and 91%, respectively. So far, many preparation methods, such as carbon-coating [6], [7], metal-doping [8], particle-size minimizing [9], [10], [11], [12], can be used to overcome these problems on a certain extent. Nevertheless, the oxidization of Fe2+ into Fe3+ is often encountered during preparation process [1], [10], [11] even if the LiFePO4 cathode material is prepared at a reducing atmosphere or using reductive agent, thus giving rise to the negative effect for the electrochemical performance. Subsequently, it is of significance to eliminate or reduce the negative effect for better electrochemical performances.
In the present work, the LiFePO4/C cathode materials were synthesized by hydrothermal synthesis without and with magnetic treatment. The purpose of the investigation is to understand the magnetic treatment for the removal of Fe3+ cations from the LiFePO4/C cathode material during the preparation process by microstructure characterization and electrochemical measurements.
Section snippets
Experiments
LiFePO4/C composite was synthesized by hydrothermal synthesis. The LiOH·H2O (90%), H3PO4 (85%), FeSO4·7H2O (99%) and C6H12O6 were used as raw materials for the preparation of the LiFePO4/C cathode material. Firstly, LiOH·H2O (2.797 g) and H3PO4 (2.306 g) were respectively dissolved in 20 ml and 5 ml distilled water, then H3PO4 solution was added to LiOH·H2O slowly and the two solutions reacted for 45 min to prepare Li3PO4. Secondly, FeSO4·7H2O (5.560 g) was dissolved in 30 ml distilled water with
Results and discussion
Fig. 1 is the XRD patterns of the LiFePO4/C composites synthesized without and with magnetic treatment. Evidently, the diffraction peaks for the composites are in good agreement with LiFePO4. The lattice parameter and cell volume of the LiFePO4/C composite calculated with JAD 5 software are given in Table 1. The lattice parameter a of the LiFePO4/C composite synthesized with magnetic treatment is 1.0339 nm which is larger than that of LiFePO4/C composites synthesized without magnetic treatment
Conclusions
The LiFePO4/C composite with better electrochemical performances was prepared by the hydrothermal synthesis method with magnetic treatment. The capacity retention can reach up to 100% at the 100th cycle number at 1 C and 5 C. Magnetic treatment can remove Fe3+ cations effectively during preparation and enhance the cycle life of LiFePO4/C cathode material.
Acknowledgments
This work was supported by the Foundation of State Key Laboratory of Rare Earth Resources Utilization (RERU2013021).
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