Preparation of xLiFePO4·yLi3V2(PO4)3/C Composite Cathode Materials Using Simple Physical Blending Process

Abstract

In this study, lithium iron phosphate/carbon (LiFePO4, LFP) and lithium vanadium phosphate/carbon (Li3V2(PO4)3, LVP) cathode materials were synthesized by solid-state method. Then, the prepared LFP and LVP were physical blending by spray drying followed a carbon coating calcination process to obtain the lithium iron phosphate-lithium vanadium phosphate/carbon composite cathode materials (xLiFePO4·yLi3V2(PO4)3/C, xLFP·yLVP/C) under different molar ratio (x:y =1:0, 3:7, 4:6, 5:5, 6:4, 7:3, 0:1) ) of LFP and LVP. The results showed that the initial discharge capacity of LFP and LVP at 0.1C/0.1C was 147.92 mAh/g (2.4-3.8 V) and 124.51 mAh/g (2.4-4.3 V), respectively. For the composite cathode materials with different molar ratio of LFP and LVP, the initial discharge capacity at 0.1C/0.1C (2.8-4.3 V) was 121.43 mAh/g for 3LFP·7LVP/C, 122.63 mAh/g for 4LFP·6LVP/C, 130.38 mAh/g for 5LFP·5LVP/C, 137.05 mAh/g for 6LFP·4LVP/C, 137.53 mAh/g for 7LFP·3LVP/C , respectively. The results showed that 0.7LFP·0.3LVP/C composite cathode materials delivered the best initial discharge capacity of 137.53 mAhg-1 at 0.1C/0.1C, 126.98 mAh/g at 0.2C/0.2C, 123.81 mAh/g at 0.2C/0.5C, 118.58 mAh/g at 0.2C/1C, and 69.55 mAh/g at 0.2C/3C, respectively. For the cyclic stability testing, the discharge capacity of 0.7LFP · 0.3LVP/C composite cathode material decreased from 135.02 mAh/g to 129.28 mAh/g after 50 cycles at 0.1C/0.1C and room temperature (25℃), the capacity retention rate was 95.75%. Moreover, the discharge capacity of 0.7LFP·0.3LVP could be maintained 105.16 mAh/g after 50 cycles at 0.1C/1C and low temperature (-20℃). No obvious capacity fading could be observed. The results showed that prepared 0.7LFP·0.3LVP/C composite cathode materials prepared from a simple physical blending by spray drying followed a calcination had a good electrochemical properties as compared with those of pure LFP/C and LVP/C cathode materials.