Effect of Environmental Temperature on the Content of Impurity Li(3)V(2)(PO(4))(3)/C in LiVPO(4)F/C Cathode for Lithium-ion Batteries

Previous studies have shown that the impurity Li(3)V(2)(PO(4))(3) in LiVPO(4)F will adversely affect its electrochemical performance. In this work, we show that the crystalline composition of LiVPO(4)F/C is mainly influenced by the environmental temperature. The content of Li(3)V(2)(PO(4))(3) formed in LiVPO(4)F/C is 0, 11.84 and 18.75% at environmental temperatures of 10, 20, and 30°C, respectively. For the sample LVPF-30C, the SEM pattern shows a kind of alveolate microstructure and the result of selected area electron diffraction shows two sets of patterns. The LiVPO(4)F/C cathode without impurity phase Li(3)V(2)(PO(4))(3) was prepared at 10°C. The selected area electron diffraction result proves that the lattice pattern of LiVPO(4)F is a regular parallelogram. Electrochemical tests show that only one flat plateau around 4.2 V appears in the charge/discharge curve, and the reversible capacity is 140.4 mAh·g(−1) at 0.1 C, and 116.3 mAh·g(−1) at 5 C. From these analyses, it is reasonable to speculate that synthesizing LiVPO(4)F/C at a low environmental temperature is a practical strategy to obtain pure crystalline phase and good electrochemical performance.