Effect of environmental temperature on the content of impurity Li3V2(PO4)3/C in LiVPO4F/C cathode for lithium ion batteries

摘要

Abstract: Some previous studies show that the impurity Li3V2(PO4)3 in LiVPO4F will sacrifice its electrochemical performance. In this paper, we prove that the crystalline composition of LiVPO4F/C is mainly influenced by the environmental temperature. The content of Li3V2(PO4)3 formed in LiVPO4F/C is 0, 11.84 % and 18.75 % at environmental temperature of 10, 20, 30 ?C, respectively. For the sample LVPF-30C, SEM pattern shows a kind of alveolate microstructure and results of selected area electron diffraction (SAED) is composed of two sets of patterns. LiVPO4F/C cathode without impurity phase Li3V2(PO4)3 was prepared at 10 ?C. SAED results proves that the lattice pattern of it is the regular parallelogram. Electrochemical tests shows 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 LiVPO4F/C at a low environmental temperature is a practical strategy to obtain the pure crystallite phase and good electrochemical performance.