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, SiO2 was adopted to modify the composite films with various filling proportions by solution method. Results of DSC and XRD tests showed that SiO2 nanoparticles could significantly reduce the crystallinity of the films, but hardly changed the morphology of PVDF. With an increase in SiO2 content, both porosity and electrolyte uptake rate for the composite films increased, but an excessive loading of SiO2 tended to agglomerate inside the films. The porosity and electrolyte uptake rate for composite film containing 3% SiO2 were found to be the highest. As SiO2 loading increased, both first charge-discharge capacity and efficiency of the composite films were enhanced with the discharge cycle stability enhanced simultaneously. When 3% SiO2 was incorporated, the PVDF/PMMA/SiO2 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.