A water-based Al₂O₃ ceramic coating for polyethylene-based microporous separators for lithium-ion batteries

To develop an environmentally friendly and cost-effective water-based inorganic coating process for hydrophobic, polyolefin-based microporous separators, the effect of surfactants in an aqueous inorganic coating solution comprising alumina (Al₂O₃) on polyethylene (PE)-based microporous separators is investigated. By using a selected surfactant, i.e., disodium laureth sulfosuccinate (DLSS), the aqueous Al₂O₃ coating solution maintained a dispersed state over time and facilitated the formation of a uniform Al₂O₃ coating layer on PE separator surfaces. Due to the hydrophilic nature of the Al₂O₃ coating layers, the as-prepared, ceramic-coated PE separators had better wetting properties, greater electrolyte uptake, and larger ionic conductivities compared to those of the bare PE separators. Furthermore, half cells (LiMn₂O₄/Li metal) containing Al₂O₃-coated PE separators showed improved capacity retention over several cycles (93.6% retention after 400 cycles for Al₂O₃ coated PE separators, compared to 89.2% for bare PE separators operated at C/2) and rate capability compared to those containing bare PE separators. Moreover, because the Al₂O₃-coated layers are more thermally stable, the coated separators had improved dimensional stability at high temperatures (140 °C).