Microporous Cyclodextrin Film with Funnel-type Channel Polymerized on Electrospun Cellulose Acetate Membrane as Separators for Strong Trapping Polysulfides and Boosting Charging in Lithium–Sulfur Batteries

The “shuttle effect” of polysulfides hampers the commercialization of lithium–sulfur (Li-S) batteries. Here, a thin molecular sieve film was decorated on the surface of an electrospun cellulose acetate (CA) membrane derived from recycled cigarette filters, where the truncated cone structure β-cyclodextrin (β-CD) was selected as the building block to physically block and chemically trap polysulfides while simultaneously dramatically speeding up ion transport. Furthermore, on the β-CD free side of the separator facing the cathode, graphite carbon (C) was sputtered as an upper current collector, which barely increases the thickness. These benefits result in an initial discharge performance of 1378.24 mAh g⁻¹ and long-term cycling stability of 863.78 mAh g⁻¹ after 1000 cycles at 0.2 C for the battery with the β-CD/CA/C separator, which is more than three times that of the PP separator after 500 cycles. Surprisingly, the funnel-type channel of β-CD generates a differential ionic fluid pressure on both sides, speeding up ion transport by up to 69%, and a 65.3% faster charging rate of 9484 mA g⁻¹ was achieved. The “funnel effect” of a separator is regarded as a novel and high-efficiency solution for fast charging of Li-S and other lithium secondary batteries.