Close-Packed Al<sub>2</sub>O<sub>3</sub> Nanoparticles/Waterborne Polyurethane Layer-Coated Polyethylene Separators for Lithium-Ion Batteries

Abstract

Separator shutdown by interrupting the transmission of lithium ions to terminate the battery reaction is a valid safety mechanism for preventing thermal runaway reactions in lithium ion batteries. Yet the cell temperature continues rising after the shutdown, the separator need sufficient thermal stability to physically isolate the electrodes. To reduce the thermal shrinkage of polyethylene (PE) separators, a fresh composite separator is developed by introducing alumina (Al2O3) nanoparticles/waterborne polyurethane (WPU) layer on one side of the pristine PE separator via casting process. The microporous structure of the composite separator is supposed to be a significant consideration for the cell performance, which is confirmed by the scanning electron microscope. Compared with the pristine PE separator, the thermal shrinkage of the novel separator improved markedly with an acceptable decline in air permeability and ion conductivity.