Microporous membranes of NaY zeolite/poly(vinylidene fluoride–trifluoroethylene) for Li-ion battery separators

Microporous membranes based on poly(vinylidene fluoride–trifluoroethylene) with different NaY zeolite contents were prepared by solvent casting at room temperature for lithium ion battery separator applications. The dependence of the polymer porous microstructure with increasing zeolite content is evaluated as well as the thermal, mechanical and electrical properties of the membrane before and after uptake of the electrolyte solution of 1M LiClO4·3H2O-PC. The zeolite fillers are placed in the walls of the membranes and do not influence significantly the porosity of the membranes. On the other hand, the fillers improve the mechanical strength of polymeric matrix and increase their ionic conductivity. The electrolyte with 16 wt.% of zeolites is thermally stable up to 100 °C and exhibits the highest conductivity over the studied range of temperatures (2.33 × 10−6 and 2.51 × 10−2 S cm−1 at 20 and 120 °C, respectively). According to infrared spectroscopic data, major modifications occur in terms of hydrogen bonding interactions at this composition. All porous membranes show good electrochemical stability as determined by cycle voltammetry. The electrochemical stability domain of the sample with 16 wt.% zeolite content spans about 5.5 V versus Li/Li+.