Study on Influencing Factors of Calendar Aging and Cycle Aging of LFP Batteries

Lithium iron phosphate (LFP) batteries are widely deployed in electric vehicles and large-scale energy storage systems due to their low cost, high safety, and excellent cycling stability. However, long-term operation introduces aging phenomena that critically limit performance and lifetime. In this study, multi-condition calendar and cycle aging tests were performed to elucidate the effects of storage state of charge (SOC), temperature, pressure, and cycling protocols on degradation. The results show that calendar aging is strongly governed by SOC and temperature, with higher SOC and elevated temperature accelerating capacity fade via enhanced SEI growth, while pressure exerts a negligible influence. Notably, under different SOC storage conditions, when the batteries are aged to the same state of health (SOH), the largest increase in Direct Current Resistance (DCR) is observed for the batteries stored at 50% SOC. For cycle aging, degradation is dominated by charging rate, SOC window, and temperature, whereas discharge rate and pressure have only minor effects. High-rate charging at low temperature induces lithium plating and rapid capacity loss, while wider or higher SOC cycling ranges significantly accelerate fade and stress accumulation. Overall, this work systematically identifies the key operational factors shaping LFP battery degradation, clarifies their underlying mechanisms, and provides theoretical guidance for optimizing usage strategies to enhance durability under complex operating conditions.