Repelling polysulfide ions by boron nitride nanosheet coated separators in lithium-sulfur batteries

Migration of cycling intermediates (polysulfides) from the cathode to anode through a separator is one of the main problems in current lithium-sulfur batteries that deteriorates cycling performance of the cell. Here we report a multifunctional separator, which is constructed by incorporation of functionalized boron nitride nanosheets with negatively charged groups onto a commercial Celgard separator. The boron nitride separator is capable to prevent polysulfide migration through the separator effectively due to strong ion repelling of negatively charged polysulfides by the negatively charged boron nitride nanosheets. The lithium-sulfur cell with a boron nitride separator exhibits an excellent long-term cycling stability up to 1000 cycles and a high capacity of 718 mA h g -1 at a very high current of 7 C (1.18 A g -1 ). Such an excellent high rate capacity and long-term stability of the cell are certainly contributed by the boron nitride separators that inhibit internal redox shuttle and increase the diffusion coefficient of lithium ions.