A facile method to enhance the uniformity and adhesion properties of water-based ceramic coating layers on hydrophobic polyethylene separators

Highlights: • Polydopamine-treated PE separators were used for ceramic-coated separators (CCSs). • Polydopamine (PDA) facilitated the uniform water-based ceramic coating layers. • PDA-PE/CCS improved adhesion strength between PE and ceramic coating layers. • PDA-PE/CCS improved thermal stability compared to bare PE. • PDA-PE/CCS improved rate and cycle retention abilities of full cells. To enhance the uniformity and adhesion properties of water-based ceramic coating layers on hydrophobic polyethylene (PE) separators, their surfaces were treated with thin and hydrophilic polydopamine layers. As a result, an aqueous ceramic coating slurry consisting of Al₂O₃ particles, carboxyl methyl cellulose (CMC) binders, and water solvent was easily spread on the separator surface, and a uniform ceramic layer was formed after solvent drying. Moreover, the ceramic coating layer showed greatly improved adhesion properties to the PE separator surface. Whereas the adhesion strength within the bulk coating layer (F_mid) ranged from 43 to 86 N m⁻¹ depending on the binder content of 1.5–3.0 wt%, the adhesion strength at the interface between the ceramic coating layer and PE separator (F_sepa-Al2O3) was 245–360 N m⁻¹, a value equivalent to an increase of four or five times. Furthermore, an additional ceramic coating layer of approximately 7 μm did not degrade the ionic conductivity and electrochemical properties of the bare PE separators. Thus, all the LiMn₂O₄/graphite cells with ceramic-coated separators delivered an improved cycle life and rate capability compared with those of the control cells with bare PE separators.