Oxygen vacancy-rich MnO nanoflakes/N-doped carbon nanotubes modified separator enabling chemisorption and catalytic conversion of polysulfides for Li-S batteries

Abstract

A modified separator for improving the electrochemical performance in Li-S batteries is fabricated by functional composites coating, comprised of MnO nanoflakes with rich oxygen vacancies and N doped carbon nanotubes (MnO-OVs/NCNTs). On the one hand, MnO as a polar material can anchor lithium polysulfides (LiPSs) on the interface via chemical bonding. In addition, introducing oxygen vacancies into MnO by heat treatment under a reducing atmosphere can regulate the electronic structure and provide extra active sites for further boosting the chemical adsorption capability of LiPSs, facilitating the redox reaction of LiPSs, as well as enhancing the electron transfer efficiency. On the other hand, the MnO-OVs/NCNTs layer is a barrier to block the LiPSs directly diffusing through the separator and acts as an upper collector to reduce the interface resistance reactivate the trapped sulfur species, thereby enhancing the sulfur utilization. Given these advantages, the MnO-OVs/NCNTs modified separator employed in Li-S batteries exhibit considerable capacity (1516 mAh g−1 at 0.1C), enhanced long-term cycling stability (capacity retention of 618 mAh g−1 for over 500 cycles at 1C), and rate performance (550 mAh g−1 at 3C).