Abstract:

Taking the square LiFePO₄ (LFP) /graphite power battery as the research object, the failure mechanism is explored when the battery cycles with 1C current at 45℃. By dissecting the battery, the changes in the thickness, morphology, structure and gram capacity of the positive and negative plates before and after the battery cycle are systematically analyzed. With the continuous cycling of the battery at 45℃, the electrolyte in the battery is gradually decomposed, the loss of Fe dissolution is aggravated, and the growth of SEI film is accelerated, which leads to the large consumption of active lithium and the increase of EIS and battery polarization. The results indicate that the capacity loss of anode which is caused by active lithium consumption and structure change is higher than that in the cathode, which are 6.7% and 22.64%, respectively. Therefore, the battery failure is mainly resulted by the attenuation of dynamic performance of the graphite negative electrode.

Key words: power battery, LiFePO₄, electrochemistry, dynamics, film

摘要：

以电动汽车的方型LiFePO₄/石墨动力实验电池为研究对象，探究其在45℃恒温箱下1C充放电循环的失效机理。通过对电池进行解剖，系统分析了电池循环前后正负极片的厚度、形貌、结构和克容量的变化。随着电池在45℃高温下循环，电解液分解以及Fe溶出损失、SEI膜再生长，消耗大量的活性锂，交流内阻增加导致电化学极化增大，活性锂消耗引起负极容量损失为6.7%，负极结构变化造成的容量损失为22.64%。结果表明石墨负极动力学性能的衰减是电池失效的主要因素。

关键词: 动力电池, 磷酸铁锂, 电化学, 动力学, 膜