Binder-Free, Thin-Film Ceramic-Coated Separators for Improved Safety of Lithium-Ion Batteries

Separators play a crucial role in ensuring the safety of lithium-ion batteries (LIBs). Commercial polyolefin-based separators such as polyethylene (PE) still possess serious safety risks under abuse conditions because of their poor thermal stability. In this work, a novel type of binder-free, thin ceramic-coated separators with superior safety characteristics is demonstrated. A thin layer of alumina (Al₂O₃) is coated on commercial PE separators using the electron-beam physical vapor deposition (EB-PVD) technique. Scanning electron microscopy (SEM), contact angle, impedance spectroscopy, and adhesion test techniques were employed to evaluate structure-property correlations. When compared to commercial slurry-coated separators, the EB-PVD-coated separators display (i) higher thermal stability, (ii) stronger ceramic-polymer adhesion, and (iii) competitive electrochemical performance of full LIB cells. Thermal stability, in terms of improved shutdown and breakdown characteristics of the separator, was studied using the in situ impedance technique up to 190 °C. In addition, the improved adhesion of the ceramic layer deposited on the PE separator was studied following the tape adhesion strength test. We prove that the thin (binder-free) ceramic layer coated by EB-PVD is far more effective in improving separator safety than those made using the conventional thick slurry coating.