Aluminum Hydroxide-Based Flame-Retardant Composite Separator for Lithium-Ion Batteries

Despite the extensive use of polyolefins, especially in the form of lithium-ion battery (LIB) separators, their flammability limits their large-scale battery applications. Therefore, the fabrication of flame-retardant LIB separators has attracted much attention in recent years. In this work, composite separators were fabricated by applying a ceramic-based composite coating composed of a metal hydroxide as a filler and flame-retardant agent (Aluminium hydroxide, Al(OH)3) and a binder (Poly(vinylidene Fluoride-co-hexafluoropropylene), P(VDF-HFP)) to the polypropylene (PP) commercial separator. Thermal shrinkage, thickness, air permeability, porosity, wettability, ionic conductivity, flame retardancy, and electrochemical performance of the fabricated ceramic-coated composite separator were investigated. The results showed that the addition of Al(OH)3 particles improved thermal shrinkage ( 8 %) and flame retardancy of the commercial separator, which can prevent dimensional changes at high temperatures and significantly increase LIBs safety. Applied 11 µm ceramic-based coating layer on PP commercial separator had 76 % porosity that increased the value of air permeability from 278.15 (s/100 cc air) to 312.8 (s/100 cc air), causing much facile air permeation through the pores of commercial separator than the composite one. Furthermore, suitable electrolyte uptake and the contact angle of ceramic coated separator (135 % and 91.19°, respectively) facilitated ion transport through the pores, which effectively improved the ionic conductivity of Al(OH)3-coated PP separator (about 1.4 times higher than bare separator). Moreover, the cell comprising Al(OH)3-coated PP separator had better cyclic performance than that of bare PP separator. All these characteristics make the fabricated flame-retardant Al(OH)3 composite separator an appropriate candidate to ensure the safety of the large-scale LIB.