Temperature Effect on LiFePO4 Cathode Performance

Abstract

Two forms of LiFePO4 material were evaluated in lithium cells. One type of LiFePO4 (PI) that has a particle size ranging from 1-5 µm is compared to LiFePO4 (P-II) consisting of nano-particles. Coated electrodes on Al-carbon with thickness varying from 18 to 25 µm were used in this study. The addition of VGCF carbon fiber greatly improved the rate capability at low temperature. This suggests a good conductivity networking and wettability in the cathode. LiFePO4 (P-II) has improved the low- and high-rate discharge capacity. When VGCF fibers were combined with LiFePO4 (P-II) in the same composite cathode, the high rate capacity at 12C was increased by 51% compared to LiFePO4 (P-I) cathode with carbon black. At -10{degree sign}C and at 2C rate, 90 mAh/g was delivered from the cell. Cycling at 60{degree sign}C occurred with negligible capacity fade after 400 cycles. Furthermore, the cell was capable of good performance at high rate with 120 mAh/g at 10C, and it still has a good reserve at 25C with 73mAh/g.