Hsu Wen-Dung, Yang Po-Wei, Chen Hung-Yuan, Wu Po-Hsien, Wu Pin-Chin, Hu Chih-Wei, Saravanan Lakshmanan, Liao Yen-Fa, Su Yen-Teng, Bhalothia Dinesh, Chen Tsan-Yao, Chang Chia-Chin
Department of Materials Science and Engineering, National Cheng Kung University, Tainan, 70101, Taiwan.
Hierarchical Green-Energy Materials Research Center, National Cheng Kung University, Tainan, 70101, Taiwan.
Sci Rep. 2021 Jan 21;11(1):1929. doi: 10.1038/s41598-021-81644-3.
The abnormal lattice expansion of commercial polypropylene (PP)/polyethylene (PE)/polypropylene (PP) separator in lithium-ion battery under different charging current densities was observed by in-situ X-ray diffraction. Significant lattice changes of both PP and PE were found during the low current density charging. The capacity fading and the resistance value of the cell measured at 0.025 C (5th retention, 92%) is unexpectedly larger than that at 1.0 C (5th retention, 97.3%) from the electrochemical impedance spectroscopic data. High-resolution scanning electron microscopy is employed to witness the pore changes of the trilayered membrane. Density functional theory calculations were used to investigate the mechanism responsible for the irregular results. The calculations revealed that the insertion of Li-ion and EC molecule into PP or PE are thermodynamically favourable process which might explain the anomalous significant lattice expansion during the low current density charging. Therefore, designing a new separator material with a more compact crystalline structure or surface modification to reduce the Li insertion during the battery operation is desirable.
通过原位X射线衍射观察到锂离子电池中商用聚丙烯（PP）/聚乙烯（PE）/聚丙烯（PP）隔膜在不同充电电流密度下的异常晶格膨胀。在低电流密度充电过程中，发现PP和PE的晶格都有显著变化。根据电化学阻抗谱数据，在0.025 C下测量的电池容量衰减和电阻值（第5次保留率，92%）意外地大于在1.0 C下的测量值（第5次保留率，97.3%）。采用高分辨率扫描电子显微镜观察三层膜的孔隙变化。利用密度泛函理论计算来研究导致不规则结果的机制。计算结果表明，锂离子和碳酸乙烯酯（EC）分子插入PP或PE是热力学上有利的过程，这可能解释了低电流密度充电过程中异常显著的晶格膨胀。因此，设计一种具有更紧凑晶体结构的新型隔膜材料或进行表面改性以减少电池运行过程中的锂插入是很有必要的。
