Hierarchical microstructure and performance of PVDF/PMMA/SiO2 lithium battery separator fabricated by thermally-induced phase separation (TIPS)

Lithium-ion batteries (LIBs) have attracted more and more attention in recent years because of their renewable, clean energy and high-cost performance. Polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA) were expected to be used in the preparation of LIB separator due to their excellent comprehensive properties. In this work, a series of PVDF/PMMA LIB separators were prepared by thermally-induced phase separation (TIPS), which is a simple method of fabricating microporous films. In order to improve the comprehensive performance, SiO 2 was adopted to modify the composite films with various filling proportions by solution method. Results of DSC and XRD tests showed that SiO 2 nanoparticles could significantly reduce the crystallinity of the films, but hardly changed the morphology of PVDF. With an increase in SiO 2 content, both porosity and electrolyte uptake rate for the composite films increased, but an excessive loading of SiO 2 tended to agglomerate inside the films. The porosity and electrolyte uptake rate for composite film containing 3% SiO 2 were found to be the highest. As SiO 2 loading increased, both first charge–discharge capacity and efficiency of the composite films were enhanced with the discharge cycle stability enhanced simultaneously. When 3% SiO 2 was incorporated, the PVDF/PMMA/SiO 2 composite film displayed the best comprehensive performance of the battery among all film samples examined. This study presents a facile way of manufacturing LIB separators with relatively ideal overall battery performance.