磷酸铁锂电池循环过程中电化学交流阻抗研究

Electrochemical impedance analysis of LiFePO_4/C batteries in cycling process

研究了商品化磷酸铁锂电池不同倍率循环过程中的电化学交流阻抗谱,分析了电池体系中各部分阻抗随循环次数的变化规律,并对不同循环次数的正负极片表面形貌进行了表征分析。实验表明在较高倍率下电池容量衰减较快,其影响因素主要是石墨负极结构的破坏,与之相对应的是在交流阻抗谱上中低频区新出现的一段圆弧,说明交流阻抗谱的变化与电池性能劣化状态具有相关性。结果表明可以通过电化学交流阻抗谱的特征变化来判断电池的容量劣化状态,为电池的分级筛选和建立梯次利用电池快速评价系统提供了理论依据和技术支持。

The cycle performance and capacity fading of commercial LiFePO4/C batteries were studied at different rate. The electrochemical impedance spectroscopy （EIS）of the battery was tested and analyzed in different charge-discharge cycles. The morphologies of anode and cathode at different cycle numbers were also characterized by scanning electron microscope （SEM）. The experimental results show that the capacity fading of the batteries become faster at higher rate cycling. The SEM images of the cycled electrodes exhibit that capacity fading of the batteries were possibly attributed to the degradation of the anode structure. When the performance of the battery deteriorate sharply, there was a new semicircular arc appearing in the low-mid frequency region in the relative EIS, indicating that the change of EIS can correlate with the state of the battery performance degradation. Therefore, the performance characteristics of battery could be evaluated according to electrochemical impedance spectroscopy. It could also provide scientific and technical support for the fast evaluation system of battery on the cycling performance.