Hierarchical 3D nitrogen and phosphorous codoped graphene/carbon nanotubes-sulfur composite with synergistic effect for high performance of lithium-sulfur batteries

Lithium-sulfur battery has been considered as a promising electrochemical energy storage system based on its theoretical energy density. However, its practical application is hindered by poor conductivity of sulfur and the shuttle effect. Herein, a hierarchical three-dimensional nitrogen and phosphorous codoped graphene and carbon nanotubes with 70 wt% of sulfur content (N, P codoped G/CNTs-S70) composite was prepared using melamine phosphate as a single precursor of N and P. The simultaneous introduction of N and P creates high active sites on the G/CNTs backbones, restricts the detachments of sulfur from the host G/CNTs, and induces strong chemical adsorption of the dissolution of lithium polysulfides. The as-prepared N, P codoped G/CNTs-S70 composite delivers a high initial discharge capacity of 1550 mA h g(-1) and retains a capacity of 735 mA h g(-1) after 200 cycles at 0.5 C. This is a significant improvement in the rate capability and cycling stability compared with the un-doped G/CNTs-S70 cathode. This simple strategy with single precursor offers promising electrochemical properties for Li-S batteries.