Functional double-layer membrane as separator for lithium-sulfur battery with strong catalytic conversion and excellent polysulfide-blocking

Lithium-sulfur (Li-S) battery with promising specific capacity and high energy density has attracted wide attention in recent years. However, the rapid capacity fading of the batteries caused by the “shuttle effect” of soluble polysulfides restricted its applications. Here, a novel thermostable double-layer membrane based on F-doped poly-m-phenyleneisophthalamide (PMIA) membrane and F-mangano-manganic oxide (Mn3O4) co-doped PMIA membrane is fabricated through electrospinning method. The F-PMIA membrane and F-Mn3O4-co-doped PMIA membrane in the double-layer membrane can act as the matrix to prepare gel polymer electrolyte (GPE). More importantly, the F-doped PMIA membrane in combination with F-Mn3O4-co-doped PMIA membrane, render the engineered functional separator with extraordinary high electrolyte uptake and eminent preserving liquid electrolyte, excellent thermal stability and shrinkage resistance, strong catalytic conversion, forceful chemisorption and physical blocking the “shuttle effect” of lithium polysulfides for Li-S battery. Based on these merits, the assembled batteries with the novel separator exhibited a high first-cycle discharge capacity with 1237.1 mAh g−1, excellent discharge capacity retention of 814.0 mAh g−1 and high Coulombic efficiency of 98.83% after 1000 cycles at the current density of 0.5 C rate. In addition, the obtained Li-S battery with GPE presented a low interfacial resistance and high rate capacity (624.1 mA h g−1 at 2 C rate after 600 cycles). The reasons of these excellent electrochemical performances for the battery using the prepared membrane were ascribed to the suppressed “shuttle effect” through both the physical trapping of lithium polysulfides by the GPE based as matrix on F-doped PMIA membrane and chemical binding of intermediates by F-Mn3O4-co-doped membrane. The new separator will open up an effective avenue to enhance the capability and cyclability of Li-S batteries.