An efficient carbon coating process applied in different synthetic routes of LiFePO4 cathode materials

Abstract

Four LiFePO4/C composites have been successfully synthesized via Fe2O3 route, FeC2O4 route, FePO4 route in solid-state method and FeSO4 route in hydrothermal method with an efficient carbon coating process which innovatively employed compound carbon sources that consisted of fructose and calcium lignosulfonate. Kilogram grade pilot samples have been prepared and 2000 mAh pouch cells have been assembled and investigated. Due to the introduction of fructose and calcium lignosulfonate, the as-prepared LiFePO4/C composites possess a layer of conductive carbon that contains calcium compound on the surface of LiFePO4 particles, which are supposed to improve the electronic conductivity and reduce the side reaction between LiFePO4 and electrolytes. All of the as-prepared LiFePO4/C composites show different characteristics in full cells, the capacity retention of Fe2O3 derived LFP-S1 was as high as 92.2% after 400 days storage, the capacity retention of FeC2O4 derived LFP-S2 at 5C rate was 93.0%, the capacity retention of FePO4 derived LFP-S3 at -20 ° was 66.7%, the capacity retention of FeSO4 derived LFP-S4 was as high as 90.2% after 3000 cycles at 25 °.