Simultaneous optimization of surface chemistry and pore morphology of 3D graphene-sulfur cathode via multi-ion modulation

• 3D porous NSG is synthesized under ammonia and sulfide ion modulation.
• The surface chemistry and pore morphology of NSG is simultaneously optimized.
• The S@NSG cathode exhibits long cycle life and high capacity.

Lithium/sulfur (Li/S) battery is a promising next-generation energy storage system owing to its high theoretical energy density. However, for practical use there remains some key problems to be solved, such as low active material utilization and rapid capacity fading, especially at high areal sulfur loadings. Here, we report a facile one-pot method to prepare porous three-dimensional nitrogen, sulfur-codoped graphene through hydrothermal reduction of graphene oxide with multi-ion mixture modulation. We show solid evidence that the results of multi-ion mixture modulation can not only improve the surface affinity of the nanocarbons to polysulfides, but also alter their assembling manner and render the resultant 3D network a more favorable pore morphology for accommodating and confining sulfur. It also had an excellent rate performance and cycling stability, showing an initial capacity of 1304 mA h g−1 at 0.05C, 613 mA h g−1 at 5C and maintaining a reversible capacity of 462 mA h g−1 after 1500 cycles at 2C with capacity fading as low as 0.028% per cycle. Moreover, a high areal capacity of 5.1 mA h cm−2 at 0.2C is achieved at an areal sulfur loading of 6.3 mg cm−2, which are the best values reported so far for dual-doped sulfur cathodes.