Fabrication of diatomite/polyethylene terephthalate composite separator for lithium-ion battery

In this study, a composite separator was prepared by coating a diatomite/polyvinylidene fluoride (PVDF) mixed slurry on the polyethylene terephthalate (PET) nonwoven in order to apply to lithium-ion batteries. The effect of the mass ratio of diatomite/PVDF on the physical and electrochemical performance of the composite separators was investigated. SEM observation showed that the unique pores on the diatomite disk gradually became the main pores of the diatomite/PET composite separator with the increasing content of diatomite in the coating. As the content of diatomite in the diatomite/PET composite separator coating increased from 60 to 80 wt%, the porosity, liquid electrolyte absorption rate, and ionic conductivity gradually increased and reached a maximum (63.8%, 0.866 g cm−3, 1.43 mS cm−1, respectively) at the content of 80 wt%. The contact angle of the composite separators to the electrolyte gradually decreased as the content of diatomite increased and reached a minimum of 13.00° at 80 wt%. After heat treatment at 160 °C for 0.5 h, the composite separator with a diatomite content of 80 wt% shrank merely 1.17% that showed the outstanding thermal stability than the PP separator (39.60%). Furthermore the cells assembled with diatomite composite separators showed better cycle stability and C-rate performance at room temperature, which was related to the reduced interfacial resistance and decreased polarization voltage of the cells. Among them, the composite separator with diatomite/PVDF = 80/20 (w/w) showed the most excellent cell performance due to the unique pore structure of diatomite.