Novel preparation of lithium-ion battery wet-processed separator based on the synergistic effect of porous skeleton nano-Al2O3 in situ blending and synchro-draw

Routine lithium-ion battery separators with uneven micropores and poor electrolyte affinity raise ion transport barriers and become the battery-performance-limiting factors. A wet-processed separator with homogeneous porous structure and porous skeleton nano-Al2O3 in situ blending is readily prepared by thermally induced phase separation of paraffin, nano-Al2O3 and ultra-high molecular weight polyethylene (UHMWPE) in this work. SEM, ImageJ statistical analysis, porosity and Gurley calculation show that a separator that has undergone asynchronous drawing exhibits ample sturdy fibrils, heterogeneous pore size dispersion, poor permeability and strong anisotropy. However, UHMWPE deforms much more uniformly under a synchro-draw, which distinctly lessens coarse fibrils, centralizes porous construction after stretching and brings better isotropy for the separator. Additionally, nano-Al2O3 scattered in the cast film further weakens the heterogeneity of micropores stemming from the uneven thermally induced phase separation. Wettability tests and thermal diagnoses also show that nano-Al2O3 on the porous skeleton strengthens the thermal stability and electrolyte affinity of the separator. Consequently, batteries containing nano-Al2O3 composite separators show much higher electrochemical stability, ionic conductivity and Li+ transport number because of the synergistic effect of the even microvoids and nano-Al2O3 on the porous skeleton, which expedites Li+ transport and endows superior lithium-ion battery performance. (c) 2022 Society of Industrial Chemistry.