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

Abstract

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.

An image reconstruction modeling approach for micro‐fibrous network of cellulose polymer separator concerning tensile and pore properties

“…Kyeremateng et al 40 have prepared a self‐supported inorganic membrane composed of SiO 2 nano‐fibers, which has presented a porosity over 70% and tortuosity less than 1.7. Takeda et al 41 and Thorat et al 42 shared membranes with porosity around 50%, but with tortuosity of 2.1 and 2.6, respectively. The related works have indicated that the modeling and calculation of fibrous model is reasonable.…”

“…The pore tortuosity of the porous model Takeda et al 41 and Thorat et al 42 shared membranes with porosity around 50%, but with tortuosity of 2.1 and 2.6, respectively. The related works have indicated that the modeling and calculation of fibrous model is reasonable.…”

“…Kyeremateng et al40 have prepared a self-supported inorganic membrane composed of SiO 2 nano-fibers, which has presented a porosity over 70% and tortuosity less than 1.7. Takeda et al41 and Thorat et al42 shared membranes…”