Preferential lattice expansion of polypropylene in a trilayer polypropylene/polyethylene/polypropylene microporous separator in Li-ion batteries

Wen Dung Hsu, Po Wei Yang, Hung Yuan Chen, Po Hsien Wu, Pin Chin Wu, Chih Wei Hu, Lakshmanan Saravanan, Yen Fa Liao, Yen Teng Su, Dinesh Bhalothia, Tsan Yao Chen, Chia Chin Chang

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish
Article number1929
JournalScientific reports
Volume11
Issue number1
DOIs
Publication statusPublished - 2021 Dec

All Science Journal Classification (ASJC) codes

  • General

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