Polyaniline-Encapsulated Hollow Co–Fe Prussian Blue Analogue Nanocubes Modified on a Polypropylene Separator To Improve the Performance of Lithium–Sulfur Batteries

Recent studies of lithium-sulfur (Li-S) batteries have identified that a modified separator plays a critical role in challenging the capacity fading and shuttle effect of lithium polysulfides (LiPSs). Herein, we report a polyaniline-encapsulated hollow Co-Fe Prussian blue analogue (CFP@PANI) for separator modification. The open frame-like hollow CFP was synthesized via oriented attachment (OA). To improve the catalytic effect and electrical conductivity, PANI was coated on the synthesized CFP. The resulting CFP@PANI was applied on the conventional polypropylene (PP) separator (CFP@PANI-PP) with vacuum filtration. With a ketjen black/sulfur (KB/S) cathode with 66% of the sulfur load, the CFP@PANI-PP exhibited an initial capacity of 723.1 mAh g^-1 at a current density of 1 A g^-1. Furthermore, the CFP@PANI-PP showed stable cycling performance with 83.5% capacity retention after 100 cycles at 1 A g^-1. During the 100 cycles, each cycle maintained high coulombic efficiency above 99.5%, which indicates that the CFP@PANI-PP could inhibit LiPS migration to the anode side without a Li⁺ transport disturbance across the separator. Overall, the CFP@PANI-PP efficiently suppressed LiPSs, resulting in enhanced electrochemical performance. The current study provides useful insight into designing a nanostructure for separator modification of Li-S batteries.