Increasing N active sites by in-situ growing conformal CN layer in hierarchical porous carbon-based networks for fast Li transfer and polysulfide anchoring in lithium-sulfur batteries.

Various challenges remain to be overcome in lithium-sulfur (Li-S) batteries, including the volume expansion and low conductivity of sulfur, the shuttle effect of lithium polysulfides and the sluggish redox reaction in the cell. Herein, we propose a multilayered conductive framework by the in situ growth of a conformal graphene-like CN (GCN) coating on porous CNT@NC networks with carbon nanotubes (CNTs) as the core and N-doped carbon (NC) as the crosslinking shell. The abundant N in the GCN coating increased the surface N concentration of the framework from 14.38% to 18.77%, which enriched the active sites in the frameworks for the adsorption and catalysis conversion of LiPSs and LiS with a low energy barrier. Furthermore, the scalable frameworks can provide an 85% porosity for a sufficient reaction interface and accommodate the volume expansion of sulfur. The synergistic effect between GCN and the highly conductive hierarchical structure can accelerate the transport of Li and electrons as well as the diffusion of electrolyte. Benefitting from the above advantages, the Al-free CNT@NC@GCN electrode exhibits a reversible capacity of 647.6 mAh g after cycling for 450 cycles at 1C with a low capacity fading rate of 0.09% per cycle. This proposed facile strategy creates inspiring insights into the design of novel cathode materials for Li-S batteries.