Bioinspired, robust, flame retardant separator towards advanced safety lithium-sulfur batteries.

Microporous polyethylene (PE) membranes are commonly used separators in lithium-sulfur (LiS) batteries. However, these membranes suffer from severe shrinkage at high temperatures and exhibit limited physical barrier capability against polysulfides, which leads to significant shuttle effects, resulting in capacity decay and safety hazards. In the present study, we report a facile strategy to construct a coral-like CaCO composite functional layer on the PE separator surface using a polydopamine (PDA)-assisted in situ liquid-phase growth technique. This endows the separator with excellent mechanical properties, outstanding thermal shrinkage resistance, and exceptional flame retardancy. The multifunctional composite layer enables the synergistic suppression of polysulfides. The phenolic hydroxyl/amino functional groups in PDA provide chemical anchoring, effectively trapping polysulfides. Simultaneously, the coral-like porous structure of CaCO establishes a physical barrier, restricting polysulfide migration. Furthermore, owing to the nitrogen-containing flame retardancy of PDA and the barrier effect of CaCO, the composite layer demonstrates excellent flame retardancy. This composite layer enhances electrolyte wettability and promotes uniform lithium-ion transport, thereby suppressing lithium dendrite formation. These advantages enable LiS batteries employing the CaCO@PDA@PE composite separator to demonstrate significantly improved electrochemical performance. This approach results in high specific capacity, excellent rate capability, and extended cycle life. This study provides a cost-effective novel strategy of "chemical anchoring-physical barrier" synergy for developing LiS battery separators with high safety and superior electrochemical performance.