Paragenesis BN/CNTs hybrid as a monoclinic sulfur host for high rate and ultra-long life lithium–sulfur battery

Abstract

For lithium–sulfur (Li–S) batteries, it is critical to design advanced host materials with high conductivity and strong binding interactions with sulfur species to trap and convert the polysulfides efficiently. Here, we report a novel BN/CNTs hybrid with paragenesis structure, high surface area and O-doping via a one-step co-pyrolysis method. Such paragenesis structure can remarkably lower the contact resistance between non-conducting BN and conductive CNTs, and the O dopant in BN can narrow the bandgap of BN, both imparting the BN/CNTs hybrid a high conductivity of 1884 S m⁻¹. The BN/CNTs hybrid hosted sulfur shows monoclinic phase instead of the generally reported orthorhombic phase, implying a strong interaction between sulfur and the BN/CNTs hybrid. Moreover, the high surface and the O doping enable BN/CNTs hybrid to adsorb polysulfides with a superior capacity due to the polarization of electrons away from the sulfur atoms towards BN/CNTs. Thus, the BN/CNTs–sulfur cathode can deliver high specific capacity (1374 and 1068 mA h g⁻¹ at 0.2C and 1C, respectively), superior cycling stability (a constant coulombic efficiency of ∼99% and a decay rate of 0.045% per cycle along with 500 cycles at 1C) and excellent rate capability (840 mA h g⁻¹ at 4C). Moreover, it exhibits good high-sulfur-loading areal capacity (up to 4.5 mA h cm⁻²) with stable cell performance.