VOC-Free UV-Cured PEGDA Adhesive: A Clean and Robust Solution for Enhancing SiO₂–Modified Polyethylene Separators in Lithium-Ion Batteries

The poor wettability and thermal dimensional stability of conventional polyolefin lithium-ion battery separators has led to the widespread adoption of physical coating with hydrophilic inorganic nanoparticles as a modification method. Adhesives are crucial in this process. Nevertheless, commonly used adhesives exhibit limited thermal stability, and often require organic solvents or excessive amounts of water as slurry solvents. Therefore, we proposed an approach utilizing hydrophilic polyethylene glycol diacrylate (PEGDA) as the binder for nanosilica (SiO2) and small amount of deionized water as the coating slurry solvent. Through rapid UV curing, this method forms a robust and durable three-dimensional cross-linked network structure in the modified layer. As a result, the modified separator demonstrates excellent thermal stability and mechanical properties. Compared with the PE separator, the PE@SiO2 separator exhibits negligible shrinkage at 145 °C, with a notable improvement in tensile strength in both the MD and TD directions. Additionally, its puncture strength increased from 336 to 387 N. The electrochemical performance of the separator is also significantly enhanced. Batteries assembled with the PE@SiO2 separator demonstrate excellent discharge rate capacity and cycle stability. After 1000 charge–discharge cycles at 0.5 C, it retains 76.1% of its initial discharge capacity, significantly higher than the 49.1% retention observed with the PE separator. These results suggest that the environmentally friendly and efficient method of preparing PE@SiO2 separators using PEGDA as a binder represents a promising strategy for enhancing the safety and electrochemical performance of lithium-ion batteries.