Preparation of a high-purity ultrafine α-Al2O3 powder and characterization of an Al2O3-coated PE separator for lithium-ion batteries

Ultrafine α-Al2O3 particles with a high purity of 99.997% and an average size of 300–400 nm were successfully prepared via hydrothermal and jet-milling processes. The jet-milled Al2O3 powders were coated on a conventional polyethylene (PE) separator, and the effects of the Al2O3 particle size on the coating properties of the Al2O3-coated PE separator were investigated. When compared with both the Al2O3-coated PE separator containing unmilled particles (D50 = 3.75 μm) and the PE separator, the Al2O3-coated PE separator incorporating the jet-milled particles (D50 = 0.37 μm) exhibited a high porosity (60–63%) and a high electrolyte uptake (243–245%). The cell with the Al2O3-coated PE separator showed a similar rate capability and cycling performance at room temperature compared with the PE separator. Regarding the thermal behavior, the Al2O3-coated PE separator has a lower enthalpy, lower thermal shrinkage, and improved melt integrity compared with the pristine PE separator.