Performance of carbon-fiber-containing LiFePO4 cathodes for high-power applications

This paper describes the fabrication and testing of LiFePO4 cathodes for hybrid vehicle applications. The cathodes contained combinations of three different carbon conductivity additives: vapor-grown carbon fibers (CF), carbon black (CB) and graphite (GR). Cells of different carbon composition and active-material loading were tested with 10s charge and discharge pulses and found under certain conditions to meet the HEV power goals for the U.S. Advanced Battery Consortium. With all other factors held constant, cathodes with a mixture of CF+CB were found to have the best power-performance, followed by cells containing CF only and then by CB+GR. Thus, the use of carbon fibers as conductive additive was found to improve the power performance of cells compared to the baseline (CB+GR). The enhanced electrode performance due to the fibers also allows an increase in energy density while still meeting power goals. The best specific-power performance for each of the compositions investigated was found to occur around an active material loading of 1mAhcm-2. About one-third of the available energy was lost to irreversible processes when cells were pulse-charged or discharged at the maximum rate allowed by voltage-cutoff constraints.