Polydopamine/Silica Coating Enhances Electrochemical and Thermal Properties of Polyethylene Separators for Lithium–Metal Batteries

Polyethylene (PE) is widely used as a separator material in rechargeable batteries. However, its poor thermal stability restricts proper high-temperature performance and poses safety risks. Additionally, the poor wettability between PE separators and liquid electrolytes limits the rate capability and cycle stability, particularly in high-energy-density lithium–metal batteries (LMBs). To address these challenges, this work reports on strategies involving silica (SiO2)/polydopamine (PDA) coatings on commercial PE separators, allowing enhancement of their electrochemical and thermal properties for LMBs. PDA was predeposited on PE and subsequently directed the in situ sol–gel growth of SiO2, ultimately resulting in a SiO2@PDA-coated PE hybrid separator (SiO2@PDA@PE). PDA furnishes an adhesive catecholamine interlayer for conformal SiO2 nucleation; SiO2 imparts thermomechanical stabilization and homogenizes the ionic flux. Remarkably, incorporation with SiO2@PDA (0.5 wt %, denoted SiO2@PDA@PE-0.5) significantly enhances the separator’s ionic conductivity, Li+ transference number, and thermal stability. Consequently, LMBs constructed with a lithium metal anode, LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode, and the SiO2@PDA@PE-0.5 separator demonstrate improved long-term cycle stability (1000 cycles at 72.6% retention rate), high-rate capability (58.1% of 8 C over to 1 C), and high-temperature performance (at 120 °C). This work presents an effective strategy, through separator design, to enhance the electrochemical performance and high-temperature operation of LMBs.