Parameter Characterization and Low-Temperature Capacity Fade Modeling of LFP Cell Chemistry for Electric Vehicle Applications

Charging of electric vehicles (EVs) presents challenges that require continuous attention and effective solutions. Consequently, the aging and degradation of the lithium-ion (Li-ion) battery, resulting from continuous usage, is of particular concern. This paper addresses the issue by analyzing the response of a Li-ion cell to several charging protocols under various ambient conditions, with emphasis on low temperatures. A thorough investigation of the APR18650M1-A LFP/graphite cell is conducted. Several charging protocols are tested at ambient temperatures ranging from 0°C to 50°C, in 10°C increments. The variation of cell parameters, namely, terminal voltage, state of charge (SoC), core temperature, and faded capacity with internal resistance is reported. A new, computationally efficient, temperature-dependent capacity fade model valid for 0-20°C is proposed. Computational efficiency is preserved by implementing the model as a lookup table, ensuring constant-time fading rate retrieval. The capacity fade model is applied across all charging protocols. Results show that low C-rate protocols provide better thermal stability and slower degradation but require longer charging times. Furthermore, the cycle life yielded by all protocols is identified to peak at an ambient temperature of 19.8°C, offering practical insights for EV battery management strategies.