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.