Tuning pore structure of the poly(vinylidene difluoride hexafluoropropylene) membrane for improvement in rate performance of Li-oxygen battery

In this work, the poly(vinylidene difluoride hexafluoropropylene) (PVdF-HFP) membranes with tuned pore structure are prepared and used as a separator for the lithium-oxygen battery. Both oxygen and argon plasma treatments are used to tune the surface pore size and density of the membrane. The discharge capacity of the Li-O2 battery increases with the pore size and density of the membrane, nearly maximal capacity is achieved with a pore size of ca. 1.48 μm. More importantly, the Li-O2 battery using the PVdF-HFP membrane with tuned pore structure exhibits a significantly enhanced rate performance, probably due to a faster Li+ ion transport across the membrane. The highest discharge capacity of 466.1 mAh g−1 is achieved at a current density of 5 mA cm−2 for the Li-O2 battery with the PVdF-HFP thickness of 110 μm and pore size of 1.48 μm. Such a discharge capacity is about 10 times higher than that using commercial PP/PE/PP membrane. To our knowledge, it is the first report that the regulation of the pore structure of separator could significantly improve the rate performance of the Li-O2 battery, which probably provides a new way to solve the low rate characteristics for non-aqueous Li-O2 battery.