Thermal properties and structural evaluation of PE/MgO/PVA multilayer composite separators for lithium-ion batteries

Due to the widespread use of polyolefins in Li-ion battery separators, it is essential to improve their properties, including thermal stability and also their safety at high temperatures. To achieve this goal, composite-based magnesium oxide/polyvinyl alcohol layers were applied to the polyethylene commercial separator via the dip-coating method. Thermal shrinkage, thickness, air permeability, wettability, flame retardancy, safety, and electrochemical performance of the fabricated separators were investigated. The results showed the coated separator with 5wt.% MgO shrank about 9% less than the pristine PE separator at 130 °C. The contact angle of the pristine PE sample decreased from 115° to 62° and 54° for the 3wt.% MgO and 5wt.% MgO-coated samples, respectively. The safety test showed that the time elapsed to the voltage drop of the cells at 130℃ increased from nearly 4 min for pristine sample to 12.5 min for 3 wt% MgO-coated PE separators. Moreover, the cell prepared by the 3 wt% MgO showed best cyclic performance with the capacity retention of 95.8% after 100 cycles.