Enhanced sulfide chemisorption using boron and oxygen dually doped multi-walled carbon nanotubes for advanced lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have been the apple of people's eye with their high energy density and high theoretical capacity. However, challenges arising from the nature of materials have plagued the commercialization of this technology, among which the notorious shuttle effect, serious volume expansion and insulating nature of sulfur and its low order reduced products are key problems. Constructing nanocomposites of sulfur with heteroatom-doped carbon nanostructures is an efficient and promising approach. However, there are limited reports on boron and oxygen dual doping treatment used in lithium-sulfur batteries, let alone explaining an in-depth mechanism. Herein, we prepared boron and oxygen dually doped multi-walled carbon nanotubes (BO-MWNTs) as the host material for sulfur. With the successful introduction of boron and oxygen, the electrical conductivity of the carbon material is obviously increased. Furthermore, the effect of doped heteroatoms on the carbon/sulfur (C/S) composites and its mechanistic understanding are explored and confirmed via both experiments and Density Functional Theory (DFT) calculations. It is found that B and O dual dopants can offer abundant adsorptive sites and lead to strong chemisorption between the carbon and the sulfides. This dual doping treatment leads to improved cycling stability and rate capability performance of the C/S cathode. Hence, the proposed innovative mechanistic understanding of boron and oxygen doping on carbon materials is hopeful to shed light on the designing principle for advanced C/S composites.