Preparation of Poly(vinylidene fluoride) Lithium-Ion Battery Separators and Their Compatibilization with Ionic Liquid - A Green Solvent Approach

Battery separator membranes for lithium-ion batteries have been developed based on poly(vinylidene fluoride), PVDF, and using the green solvent - N,N'-dimethylpropyleneurea (DMPU). This separator presents a porous microstructure with a degree of porosity of 20% and pore size below 1 mm, showing excellent mechanical properties. Further, its ionic conductivity, tortuosity and MacMullin number values are 0.1 mS.cm(-1), 4 and 82, respectively. This PVDF separator membrane was evaluated in Li/C-LiFePO4 half-cells with electrolyte solution showing good cyclability and rate capability, with a discharge value after 50 cycles of 56 mAh.g(-1) at C, corresponding to 50% of the capacity retention. Its electrochemical performance soaked in ionic liquid presents a discharge capacity of 45 mAh.g(-1) at C/5-rate and capacity retention of 60%, respectively. Thus, this separator is an appropriate candidate for environmentally friendlier and safer lithium-ion batteries.