Probing the Roles of Polymeric Separators in Lithium-Ion Battery Capacity Fade at Elevated Temperatures
Probing the Roles of Polymeric Separators in Lithium-Ion Battery Capacity Fade at Elevated Temperatures
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DOI：
10.1149/2.0351409jes
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发表时间：
2014
影响因子：
3.9
通讯作者：
Jianchao Chen;Yongda Yan;T. Sun;Y. Qi;Xiaodong Li
中科院分区：
文献类型：
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作者：
Jianchao Chen;Yongda Yan;T. Sun;Y. Qi;Xiaodong Li
隔膜的高温机械性能对于锂离子电池的安全非常重要。然而，锂离子电池中聚合物隔膜在高温下的机械完整性仍然没有得到很好的表征。本文利用原子力显微镜（AFM）结合功率谱密度（PSD）分析和数字图像相关（DIC）技术，通过原位高温表面成像研究了PP（聚丙烯）-PE（聚乙烯）-PP夹心隔膜（Celgard 2325）随温度变化的微尺度形貌变化。 PSD 和 DIC 分析结果表明，当在 90°C 下循环时，甚至低于隔膜的关闭温度 (∼120°C) 和其自身的熔化温度 (165°C) 时，PP 相通过孔周围的纳米原纤维横向膨胀和纵向收缩，显着封闭其孔。这可能是由于纳米结构中的表面熔化效应，并且应该与尺寸相关——表面熔化温度可能随着纳米原纤维的直径而降低。因此，即使在工作温度下，也可能会发生一些孔隙闭合，这将导致容量衰减，这对于电池性能来说是不希望的。 © 2014 电化学协会。 [DOI：10.1149/2.0351409jes] 保留所有权利。
Thehightemperaturemechanicalpropertyofseparatorsisveryimportantforsafetyoflithium-ionbatteries.However,themechanical integrity of polymeric separators in lithium-ion batteries at elevated temperatures is still not well characterized. In this paper, the temperaturedependentmicro-scalemorphologychangeofPP(polypropylene)-PE(polyethylene)-PPsandwichedseparators(Celgard 2325) was studied by in-situ high temperature surface imaging using an atomic force microscope (AFM) coupled with power spectral density (PSD) analysis and digital image correlation (DIC) technique. Both PSD and DIC analysis results show that the PP phase significantly closes its pores by means of dilation of the nanofibrils surrounding the pores in the transverse direction and shrinkage in the machine direction, when cycled at 90 ◦ C, even below the separator’s shutdown temperature (∼120 ◦ C) and its own melting temperature (165 ◦ C). This is presumably due to surface melting effect in nanostructures and should be size dependent‐the surface melting temperature may decrease with the diameter of nanofibrils. Therefore, some pore closing might happen even at operating temperatures, it will lead to capacity fade that is undesired for battery performance. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0351409jes] All rights reserved.