Effect of the Stretching Process of Polyethylene Separators on Rate Capability of Lithium-Ion Batteries

• Published in: Journal of physical chemistry. C 2021-06, Vol.125 (23), p.12496-12503
• Main Authors: Takeda, Sahori, Saito, Yuria, Mukai, Takashi, Senoh, Hiroshi, Kaneko, Ikue, Yoshitake, Hideya
• Format: Article
• Language: English
• Subjects: C: Energy Conversion and Storage
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.1c01170

To improve the performance of lithium-ion batteries, it is necessary to elucidate the effect of the separator structure on the performance. In this study, we estimated the effect of the manufacturing method, particularly the stretching process, of the separator used in lithium-ion batteries, on its pathway morphology. The physical properties of the polyethylene membranes produced by the wet process by changing the stretching ratio were evaluated. To estimate the anisotropy of the cross-sectional pathway of the membranes, the anisotropy index was defined using the elastic moduli in two orthogonal directions: machine direction (MD) and transverse direction (TD). Furthermore, test cells using the membranes as separators were prepared, and their rate capabilities were investigated to evaluate the relationship between the morphology and battery performance. The rate capabilities showed a negative linear correlation with the physical properties of the membranes, particularly the Gurley value and the product of the MacMullin number and thickness. In addition, the rate capabilities decreased as the tortuosity or the anisotropy index of the membrane increased. These results suggest that by operating the stretching ratios in the MD and TD, the physical properties can be controlled, and membranes with good rate capabilities can be obtained.