Enhanced Lithium-Ion Transport and Sulfur Conversion Kinetics in Li–S Batteries via High-Dielectric Composite Separators

The development of lithium-sulfur (Li-S) batteries is hindered by lithium dendrite growth and slow sulfur redox kinetics. Here, we report a composite separator (CAFS) composed of nanocellulose fibers (NCF) and high-dielectric aluminum oxide (Al₂O₃) nanoparticles. The Al₂O₃ component produces a directional electric field under external bias, anchoring bis(trifluoromethanesulfonyl)imide (TFSI^-) anions and promoting lithium salt dissociation, which enhances lithium-ion (Li⁺) transport and stabilizes the anode. Additionally, the electric field actively interacts with lithium polysulfides (LiPSs), improving sulfur conversion kinetics and guiding uniform, three-dimensional Li₂S deposition. The CAFS separator exhibits a high Li⁺ transference number (0.776), enables ultrastable Li plating/stripping over 1000 h at 1 mA cm^-2, and ensures superior cycling performance with a capacity decay rate of only 0.002% per cycle over 500 cycles at 1 C. This work offers a scalable, low-cost, and eco-friendly strategy to accelerate the commercial viability of next-generation Li-S batteries.