Synergistic Effect of Dual-Ceramics for Improving the Dispersion Stability and Coating Quality of Aqueous Ceramic Coating Slurries for Polyethylene Separators in Li Secondary Batteries

We demonstrate that dispersion stability and excellent coating quality are achieved in polyethylene (PE) separators by premixing heterogeneous ceramics such as silica (SiO₂) and alumina (Al₂O₃) in an aqueous solution, without the need for functional additives such as dispersing agents and surfactants. Due to the opposite polarities of the zeta potentials of SiO₂ and Al₂O₃, SiO₂ forms a sheath around the Al₂O₃ surface. Electrostatic repulsion occurs between the Al₂O₃ particles encapsulated in SiO₂ to improve the dispersion stability of the slurry. The CCSs fabricated using a dual ceramic (SiO₂ and Al₂O₃)-containing aqueous coating slurry, denoted as DC-CCSs, exhibit improved physical properties, such as a wetting property, electrolyte uptake, and ionic conductivity, compared to bare PE separators and CCSs coated with a single ceramic of Al₂O₃ (SC-CCSs). Consequently, DC-CCSs exhibit an improved electrochemical performance, in terms of rate capability and cycle performance. The half cells consisting of DC-CCSs retain 93.8% (97.12 mAh g⁻¹) of the initial discharge capacity after 80 cycles, while the bare PE and SC-CCSs exhibit 22.5% and 26.6% capacity retention, respectively. The full cells consisting of DC-CCSs retain 90.9% (102.9 mAh g⁻¹) of the initial discharge capacity after 400 cycles, while the bare PE and SC-CCS exhibit 64.7% and 73.4% capacity retention, respectively.