Preparation of nanocomposite γ-Al2O3/polyethylene separator crosslinked by electron beam irradiation for lithium secondary battery

Although micro-porous membranes made of polyethylene (PE) offer excellent mechanical strength and chemical stability, they exhibit large thermal shrinkage at high temperature, which causes a short circuit between positive and negative electrodes in cases of unusual heat generation. We tried to develop a new technology to reduce the thermal shrinkage of PE separators by introducing gamma-Al2O3 particles treated with coupling agent on PE separators. Nanocomposite gamma-Al2O3/PE separators were prepared by the dip coating of polyethylene(PE) separators in gamma-Al2O3/poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP)/crosslinker (1,3,5-trially-1,3,5-triazine-2,4,6(1 H,3 H,5 H)-trione (TIT) solution with humidity control followed by electron beam irradiation. gamma-Al2O3/PVDF-HFP/ITT (95/5/2)-coated PE separator showed the highest electrolyte uptake (157%) and ionic conductivity (1.3 mS/cm). On the basis of the thermal shrinkage test, the nanocomposite gamma-Al2O3/PE separators containing TIT irradiated by electron beam exhibited a higher thermal resistance. Moreover, a linear sweep voltammetry test showed that the irradiated nanocomposite gamma-Al2O3/PE separators have electrochemical stabilities of up to 5.0 V. In a battery performance test, the coin cell assembled with gamma-Al2O3/PVDF-HFP/TIT-coated PE separator showed excellent discharge cycle performance.