Highly Catalytic Boron Nitride Nanofiber In Situ Grown on Pretreated Ketjenblack as a Cathode for Enhanced Performance of Lithium–Sulfur Batteries

To effectively avoid the shuttle effect of polysulfides between the cathode and anode, a boron nitride (BN)-Ketjenblack-xKOH@S composite (x means 1, 2, and 3 M) cathode for lithium–sulfur batteries with enhanced performance is prepared. Before immobilizing sulfur, BN is in situ grown on pretreated Ketjenblack through chemical etching and high-temperature calcination. It is indicated that Ketjenblack plays an important role in forming BN nanofibers with a diameter and length of around 10–30 nm and 5 μm, respectively. As supported by various characterization results, sulfur is not only anchored onto the surface of BN nanofibers and Ketjenblack through S–O–B and S–O–C interactions but also infiltrated into the micro-/mesopores of BN-Ketjenblack-xKOH substrates. The BN nanofibers act as not only S and polysulfide adsorbents but also as catalysts of the lithiation/delithiation process. The lithium–sulfur batteries with the BN-Ketjenblack-1KOH@S cathode deliver a first discharge capacity of 1822.5 mAh g–1 at 0.1 C, which is higher than the theoretical capacity (1675 mAh g–1) of sulfur caused by the adsorption and catalysis of BN, and an enlarged interlayer distance of graphene. Meanwhile, it also delivers an initial capacity of 1150.9 mAh g–1 and a high capacity retention of 51.6% after 1000 charge/discharge cycles at 2 C. This work provides a methodology for preparing a cathode material for multifunctional lithium–sulfur batteries with enhanced electrochemical performance.