Preparation of poly(vinylidene fluoride) lithium-ion battery separators and their compatibilization with ionic liquid - a green solvent approach

Abstract

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 µm, 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.