Enhanced Lithium-Ion Conductivity and Thermal Stability of Al₂O₃/Lithiated-Sulfonated-PEEK-Coated Separators for Lithium–Metal Batteries

Lithium–metal batteries (LMBs) have garnered significant interest due to their potential for high-energy-density applications; however, safety concerns arising from lithium (Li) dendrite formation and thermal instability of a conventional polyolefin separator pose critical challenges. In this study, we developed an advanced separator coated with lithiated-sulfonated polyether ether ketone (Li-SPEEK, LSP) and Al 2 O 3 particles to enhance the electrochemical performance and stability of LMBs. The Al 2 O 3 /LSP-coated separator demonstrates improved thermal stability, wettability, and electrolyte uptake compared with bare polyethylene (PE) separators, along with a substantially higher Li + transference number (0.87) and Li + conductivity (0.38 mS/cm). When applied in NCM811//Li cells, the Al 2 O 3 /LSP-coated separator delivers an enhanced rate capability and cycle life, maintaining 77.1% of its initial capacity after 120 cycles. These improvements are attributed to the stabilization of Li growth and suppression of dendrite formation, facilitated by the effective regulation of Li + flux by the Al 2 O 3 particles and the LSP coating layer. This study suggests that Al 2 O 3 /LSP-coated separators present a promising approach to improving the safety and performance of LMBs.