Novel Ceramic-Grafted Separator with Highly Thermal Stability for Safe Lithium-Ion Batteries

The separator is a critical component of lithium-ion batteries (LIBs), which not only allows ionic transport while it prevents electrical contact between electrodes but also plays a key role for thermal safety performance of LIBs. However, commercial separators for LIBs are typically microporous polyolefin membranes that pose challenges for battery safety, due to shrinking and melting at elevated temperature. Here, we demonstrate a strategy to improve the thermal stability and electrolyte affinity of polyethylene (PE) separators. By simply grafting the vinylsilane coupling reagent on the surface of the PE separator by electron beam irradiation method and subsequent hydrolysis reaction into the Al³⁺ solution, an ultrathin Al₂O₃ layer is grafted on the surface of the porous polymer microframework without sacrificing the porous structure and increasing the thickness. The as-synthesized Al₂O₃ ceramic-grafted separator (Al₂O₃-CGS) shows almost no shrinkage at 150 °C and decreases the contact angle of the conventional electrolyte compared with the bare PE separator. Notably, the full cells with the Al₂O₃-CGSs exhibit better cycling performance and rate capability and also provide stable open circuit voltage even at 170 °C, indicating its promising application in LIBs with high safety and energy density.