Metal organic framework modified poly(vinylidene fluoride-co-hexafluoropropylene) separator membranes to improve lithium-ion battery capacity fading

Abstract

The use of metal-organic frameworks in the separator membrane of lithium-ion batteries is an interesting subject of study for the next generation of energy storage devices. In this work, different poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) / metalorganic framework (MOF) based separators were prepared using three distinct MOFs, and the properties of these membranes were studied. The selected MOFs MOF-808, UiO66-NH2 and MIL-125 are characterized by sharing a common building block (cluster or linker) and possessing relatively similar surface areas and topologies. It is observed that there are significant variations in the porous structure of the separator membrane upon the introduction of the different MOFs. The use of MOFs reduces the resistivity of the assembled battery half-cells, leading to excellent battery performance, with high discharge capacity (145 mAh.g-1 at C/8) and prolonged lifecycle, outperforming e conventional neat polymer separators due to the structure’s stabilization effect of the MOF. Among the selected MOFs, the best results are achieved with UiO-66-NH2 based on its improved charge/discharge values due to the low resistivity value of the half-cell. The post-morten analysis shows that the MOF structure collapses during battery cycling, but that this fact does not significantly affect battery performance, as the produced nanofillers keep their role of minimizing battery capacity fading. Thus, it is demonstrated that adding MOFs to a polymeric separator structure is beneficial and suitable for highperformance battery applications.