Effect of FeSO4 purity on low temperature performance of LiFePO4/C

Abstract

LiFePO4/C was prepared by employing coprecipitation method and carbothermal reduction method using FeSO4 with different purity as the iron source. The purity of FeSO4 has a great influence on the morphology of FePO4, but has little effect on the morphology of LiFePO4/C. The cycling performance decreases with the decrease of purity, and purity has a significant effect on the specific discharge capacities at low temperature. The specific discharge capacities of the five samples at − 20 °C and 0.5 C were 85.3, 74.2, 65.5, 60.4, and 50.1 mAh g−1, and the capacity retention rates were 53.3%, 47.1%, 42.9%, 38.7%, and 31.9%, respectively. Full battery low temperature performance test results validate the test results of coin cell. The Li+ diffusion coefficients are 4.53 × 10−13, 2.02× 10−13, 4.73 × 10−14, 2.34× 10−14, and 8.56 × 10−15 cm2 s−1, respectively. DLi+ is reduced two orders of magnitude with reduction of raw material purity. This is mainly because the low-purity FeSO4 contains a large amount of Ti, which enters the LiFePO4/C crystal lattice, causing the lattice distortion to block the lithium ion diffusion channel. Therefore, improving the purity of raw materials is an important method to improve the low temperature performance of LiFePO4/C.