Water-based dual polymer ceramic-coated composite separator for high-energy-density lithium secondary batteries

A simple, eco-friendly, and effective additive-free technique for stabilizing a coating slurry, using alumina (Al2O3) inorganic particles and aqueous dual polymers—sodium carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) is developed. The slurry preparation process is optimized by determining the polymer binders (CMC/PVA) content in the ceramic slurry and studying the interaction between the polymer binders and Al2O3 ceramic particles by changing the mixing order of the slurry components. CMC effectively controls the viscosity of the slurry to maintain a stable slurry dispersion. In contrast, PVA significantly influences the formation of a uniform ceramic coating layer on the polyethylene (PE) separator. This results in a synergistic effect to produce an optimal ceramic-coated composite separator (CCS). Compared to the bare PE separators, the prepared Al2O3 CCSs display improved physical properties, such as high adhesion strength of the ceramic coating layer, thermal stability, electrolyte wettability, and increased ionic conductivity. Moreover, the CCSs exhibit enhanced electrochemical performance. Half cells (LiMn2O4/Li metal) comprising CCSs retained 96.5% (144.8 mAh g−1) of the initial discharge capacity even after 200 cycles, while bare PE separators lose their capacity rapidly after 150 cycles, retaining only 22.62% (33.5 mAh g−1) at the 200th cycle.