Developing uniform ceramic-coated separators in high-energy Li secondary batteries has been a challenging task because aqueous ceramic coating slurries have poor dispersion stability and coating quality on the hydrophobic surfaces of polyolefin separators. In this study, we develop a simple but effective strategy for improving the dispersion stability of aqueous ceramic coating slurries by changing the mixing order of the ceramic slurry components. The aqueous ceramic coating slurry comprises ceramics (Al2O3), polymeric binders (sodium carboxymethyl cellulose, CMC), surfactants (disodium laureth sulfosuccinate, DLSS), and water. The interaction between the ceramic slurry components is studied by changing the mixing order of the ceramic slurry components and quantitatively evaluating the dispersion stability of the ceramic coating slurry using a Lumisizer. In the optimized mixing sequence, Al2O3 and DLSS premixed in aqueous Al2O3-DLSS micelles through strong surface interactions, and they repel each other due to steric repulsion. The addition of CMC in this state does not compromise the dispersion stability of aqueous ceramic coating slurries and enables uniform ceramic coating on polyethylene (PE) separators. The prepared Al2O3 ceramic-coated separators (Al2O3–CCSs) exhibit improved physical properties, such as high wettability electrolyte uptake and ionic conductivity, compared to the bare PE separators. Furthermore, Al2O3–CCSs exhibit improved electrochemical performance, such as rate capability and cycling performance. The half cells (LiMn2O4/Li metal) comprising Al2O3–CCSs retain 90.4% (88.4 mAh g−1) of initial discharge capacity after 150 cycles, while 27.6% (26.4 mAh g−1) for bare PE. Furthermore, the full cells (LiMn2O4/graphite) consisting of Al2O3–CCSs exhibit 69.8% (72.2 mAh g−1) of the initial discharge capacity and 24.9% (25.0 mAh g−1) for bare PE after 1150 cycles.