High-content Co-Nx sites on carbon nanotubes for effective sulfur catalysis in lithium–sulfur batteries

Abstract

Multiwall carbon nanotubes (MWCNT) with high content Co-Nx coordination sites uniformly dispersed on the surface are synthesized and used as a high efficiency catalytic material in lithium-sulfur battery cathodes. The improved contents and dispersity of the Co-Nx active sites originate from the utilization of a tetraaminophthalocyanine precursor that is chemically bonded with the MWCNT. This significantly improves the exposure of the Co-Nx active sites to the active sulfur species. Density functional theory calculations reveal that the Co-Nx sites exhibit dual lithiophilic/sulfiphilic binding with polysulfides. Promoted sulfur conversion kinetics were obtained, that enabled significantly improved sulfur utilizations, high-rate capability, and cycling stability. Specific capacities of 1303 and 759 mAh g−1 were achieved at 0.2 and 3 C, respectively. Low capacity decay along cycling was also enabled, with 925 mAh g−1 retained after 500 charge/discharge cycles at 0.5 C.