Multi‐scale modelling of the tensile behavior of lithium ion battery cellulose separator

Abstract

As a satisfactory green material for a lithium ion battery separator, cellulose possesses better wettability and superior thermal and chemical stability compared to commercial polyolefin separators. The macroscopic mechanical properties of the separator are determined by structural parameters on different dimensional scales. In this paper, a two-scale modelling method is proposed for a cellulose separator. At micro-scale, a single fiber structural model was established with a cross-sectional profile extracted through image processing, combined with the fiber helix angle. At meso-scale, a representative volumetric element model and a two-dimensional random fibrous model for the fibrous network of the cellulose separator were developed. The elastic modulus in the machining direction (MD) and transverse direction (TD) of the two models were calculated by finite element simulation and compared with experimental data. The results show that the elastic modulus of the models is slightly larger than that from experiments. Compared to experiments, the relative errors in the MD and TD of the representative volumetric element model are 2.80% and 6.78%, respectively. The relative errors in the MD and TD of the two-dimensional random fibrous model are 6.70% and 8.47%, respectively. Consequently, multi-scale modelling is proven to have considerable value in investigating the properties of fibrous materials.

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

“…Subsequently, the method of computational homogenization has been proposed by some researchers 33–35 . The longitudinal elastic modulus of the fiber is set to E Longitudinal = 11.71 MPa 24 . The transverse elastic modulus is set to E Transverse_major = 2500 MPa, E Transverse_minor = 350 MPa 34 .…”

“…[33][34][35] The longitudinal elastic modulus of the fiber is set to E Longitudinal = 11.71 MPa. 24 The transverse elastic modulus is set to E Transverse_major = 2500 MPa, E Transverse_minor = 350 MPa. 34 And then the Young's modulus of the material applied is calculated by Ref.…”

“…The cellulose separator is constructed by inter‐connected fibrous network. The structure of single fiber has been studied by researchers, 17,24,25 and they have unveiled the effect of cellulose fibers on the performance of cellulose separators. Based on the parameters of a single fiber, some researchers have built a two‐dimensional woven fiber structure, during which the interference of surrounding fibers is taken into consideration 24,26,27 .…”

“…The structure of single fiber has been studied by researchers, 17,24,25 and they have unveiled the effect of cellulose fibers on the performance of cellulose separators. Based on the parameters of a single fiber, some researchers have built a two‐dimensional woven fiber structure, during which the interference of surrounding fibers is taken into consideration 24,26,27 . Some have proposed a random three‐dimensional fiber structure for reconstruction of fibrous membrane based on DIP 28–30 …”

“…Based on the parameters of a single fiber, some researchers have built a two-dimensional woven fiber structure, during which the interference of surrounding fibers is taken into consideration. 24,26,27 Some have proposed a random three-dimensional fiber structure for reconstruction of fibrous membrane based on DIP. [28][29][30] Nonetheless, further work needs to be carried out to comprehensively characterize the effect of fibrous network features.…”