In Situ-Derived Bi4Ti3O12-Bi2S3 Ferroelectric-Semiconductor Heterojunction as a Multifunctional Separator Coating for Lithium–Sulfur Batteries

The practical viability of lithium–sulfur batteries (LSBs) is severely hindered by sluggish liquid–solid conversion kinetics and the polysulfide shuttle effect. Herein, we report an in situ-derived ferroelectric-semiconductor Bi4Ti3O12-Bi2S3 heterojunction as a multifunctional separator coating. The intimate atomic-level coupling at the heterointerface generates a built-in electric field that, synergizing with the spontaneous ferroelectric polarization of Bi4Ti3O12, structurally intensifies polysulfide chemisorption and lowers the activation energy for bi-directional Li2S precipitation/dissociation. Furthermore, the localized polar field appears to homogenize lithium-ion flux, which may contribute to improved lithium anode stability. Consequently, cells featuring the modified separator deliver a high initial capacity of 1172 mAh g−1 at 0.5 C and demonstrate good cycling stability over 500 cycles with a low capacity decay rate of 0.096% per cycle. This in situ interfacial engineering offers a promising kinetic regulatory strategy for improving the performance of LSBs.