In Situ Growth Strategy to Construct “Four‐In‐One” Separators with Functionalized Polyphosphazene Coatings for Safe and Stable Lithium–Sulfur Batteries

Abstract Lithium–sulfur batteries (LSBs) are facing many challenges, such as the inadequate conductivity of sulfur, the shuttle effect caused by lithium polysulfide (LiPSs), lithium dendrites, and the flammability, which have hindered their commercial applications. Herein, a “four‐in‐one” functionalized coating is fabricated on the surface of polypropylene (PP) separator by using a novel flame‐retardant namely InC‐HCTB to meet these challenges. InC‐HCTB is obtained by cultivating polyphosphazene on the surface of carbon nanotubes with an in situ growth strategy. First, this unique architecture fosters an enhanced conductive network, bolstering the bidirectional enhancement of both ionic and electronic conductivities. Furthermore, InC‐HCTB effectively inhibits the shuttle effect of LiPSs. LSBs exhibit a remarkable capacity of 1170.7 mA h g −1 at 0.2 C, and the capacity degradation is a mere 0.0436% over 800 cycles at 1 C. Third, InC‐HCTB coating serves as an ion migration network, hindering the growth of lithium dendrites. More importantly, InC‐HCTB exhibits notable flame retardancy. The radical trapping action in the gas phase and the protective effect of the shielded char layer in the condensed phase are simulated and verified. This facile in situ growth strategy constructs a “four‐in‐one” functional separator coating, rendering InC‐HCTB a promising additive for the large‐scale production of safe and stable LSBs.