Cycling degradation of an automotive LiFePO 4 lithium-ion battery

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Degradation of a high capacity prismatic LiFePO 4 cell with deep cycling at elevated temperature of 50 °C is studied by electrochemical impedance spectroscopy as well as capacity and power fading characterization at different test temperatures (45, 25, 0 and −10 °C). Capacity fade after 600 cycles is 14.3% at 45 °C and 25.8% at −10 °C. There is little power fade at 45 °C after 600 cycles, whereas the power fade after 600 cycles is 61.6% and 77.2%, respectively, at 0 and −10 °C. The capacity and power fade evidently becomes more severe at lower temperature. In particular, the power fade at low temperatures (e.g., 0 and −10 °C) rather than capacity loss is a major limitation of the LiFePO 4 cell. The primary mechanism for capacity fade is loss of cyclable lithium in the cell resulting from lithium-consuming solid electrolyte interphase (SEI) layer growth and side reactions. The increased interfacial resistance ( R w) due to the catalytic growth of SEI layer on the graphite anode and increased electrolyte resistance are the main sources for power fade.