Building High Performance Li-S Batteries by Compositing Nanosized Sulfur and Conductive Adsorbent within MWCNTs

Abstract

Lithium sulfur batteries (Li-S) are considered to be the next generation high energy density storage system. But the polysulfide dissolution and intrinsic insulation of sulfur cause problems such as poor rate performance, low coulombic efficiency and short cycle life. To build both high rate and long life sulfur cathodes, we combine nanosized sulfur crystals and Li+/electron conductive black phosphorus (BP) with multi-walled carbon nanotubes (MWCNTs-BP/S) through two-step deposition process. Nanosized sulfur crystals could shorten Li+/electron transport routes and the cross-linked MWCNTs skeleton supports stable and super conductivity of whole cathodes. What's more, the Li+ diffusion and reaction kinetics of sulfur cathodes are greatly promoted by BP nanoparticles due to its good electronic conductivity and high Li+ diffusion constant. Meanwhile, the polysulfide diffusion is effectively restrained through chemisorption of P-S bonds. As a result, the MWCNTs-BP/S cathode with 70 wt% sulfur exhibits a stable working state over 1000 cycles at 1 C with a fading rate as low as 0.053%. Even at an ultrahigh rate of 8 C, the specific capacity still remain 505 mA h g−1. Our research proves that applying polysulfide adsorbents with both good Li+/electronic conductivity is effective for improving reaction kinetics.