高温日历老化下磷酸铁锂电池安全性能演变规律分析

Safety Performance Evolutionary Pattern Analysis of Lithium Iron Phosphate Batteries Under High-Temperature Calendar Aging Conditions

摘要

磷酸铁锂(LiFePO₄)电池因其高安全性、长循环寿命和良好的热稳定性,广泛应用于电动车辆和电化学储能系统中．然而,磷酸铁锂电池在长时放置不工作的过程中,面临着日历老化导致其容量衰减和安全性能下降的问题．为了揭示磷酸铁锂电池由于长期搁置老化导致的安全性能演变规律,本文开展了高温日历老化下磷酸铁锂电池容量衰减及安全性能的测试及分析,首先,在设计210 d高温搁置加速老化实验的基础上,利用电化学阻抗谱(EIS)结合弛豫时间分布(DRT)处理的方法,对长时高温搁置磷酸铁锂电池的容量衰减机制进行了分析．其次,为了揭示高温搁置下电池安全性能与容量衰减的关系,在电池老化过程的不同阶段开展了热失控行为的测试,同时对不同容量衰减程度的电池电极材料进行了表征分析．测试及分析结果表明,磷酸铁锂电池高温搁置容量衰减的主要表现是电池欧姆阻抗和扩散阻抗显著增加,电池的热失控触发温度(θ₂)随老化程度的增加略微升高,而热失控最高温度(θ₃)随老化程度的增加而逐渐下降．电池原位观测显示,正极活性物质的损失是电池高温日历老化条件下安全性能退化的关键因素．研究结果为高温日历老化场景下磷酸铁锂电池容量衰退和安全性能评估提供了一定的参考依据．

Abstract

Lithium iron phosphate(LiFePO₄)batteries have become a prevalent energy storage solution in electric vehicles and electrochemical energy storage systems due to their high safety,long cycle life,and good thermal stability. However,these batteries encounter issues of capacity degradation and a decline in safety performance due to calendar aging during prolonged periods of inactivity. This paper investigates the evolution of safety performance due to long-term storage aging. To this end,the capacity degradation and safety performance of LiFePO₄ batteries under high-temperature calendar aging were tested and analyzed. Initially,the design of a 210-day high-temperature storage accelerated aging experiment was employed. Electrochemical impedance spectroscopy(EIS)in conjunction with the distribution of relaxation times(DRT)method was used to analyze the mechanism of capacity degradation in LiFePO₄ batteries under prolonged high-temperature storage. Subsequently,to elucidate the correlation between safety performance and capacity degradation under high-temperature storage conditions,experiments were conducted to examine the thermal runaway behavior at various stages of battery aging. In addition,a characterization of the electrode materials of batteries with varying degrees of capacity degradation was performed. Results indicate that the primary manifestation of capacity degradation in LiFePO₄ batteries during high-temperature storage is a substantial increase in both the battery’s ohmic and diffusion impedance. The thermal runaway triggering temperature(θ₂)of the battery increases marginally with the degree of aging,whereas the maximum temperature of thermal runaway(θ₃)gradually decreases as aging progresses. In-situ observations of the battery demonstrate that the loss of the cathode active material is the primary factor in the degradation of safety performance under high-temperature calendar aging conditions. These findings establish a foundation for assessing the capacity degradation and safety performance of LiFePO₄ batteries under high-temperature calendar aging conditions.

关键词

磷酸铁锂电池 / 高温老化 / 安全性能 / 容量衰减 / 热失控

Key words

LiFePO₄ battery / high-temperature aging / safety performance / capacity degradation / thermal runaway

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基金资助

国家自然科学基金资助项目(52277214)

天津市自然科学基金资助项目(24JCZDJC00370)