Effect of Al₂O₃ coatings prepared by RF sputtering on polyethylene separators for high-power lithium ion batteries

In this study, we demonstrated the effects of aluminum oxide (Al₂O₃)-based ceramic coatings deposited by radio-frequency (RF) magnetron sputtering on commercial polyethylene (PE) microporous separators. Due to the superb thermal stability of the ceramic materials themselves, the Al₂O₃ coatings solved the chronic thermal shrinkage problem of PE separators. Separators with sputtered Al₂O₃ coatings maintained their initial dimensions even after high temperature exposure at 140 °C for 30 min. The sputtered Al₂O₃ layer effectively changed the surface of a PE separator from being hydrophobic to hydrophilic too, improving its wettability with liquid electrolyte. Additionally, a sputtered Al₂O₃ coating can improve the rate capability (~130%) compared with a bare PE separator under a high current density (7.75 mA cm^-2, 5 C rate) because the layer does not require additional use of polymeric binder materials, which usually inhibit the formation of pore structures in microporous membranes.

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