Nitrogen-doped graphene sheets were prepared through a hydrothermal reduction of colloidal dispersions of graphite oxide in the presence of hydrazine and ammonia at pH of 10. The effect of hydrothermal temperature on the structure, morphology, and surface chemistry of as-prepared graphene sheets were investigated though XRD, N(2) adsorption, solid-state (13)C NMR, SEM, TEM, and XPS characterizations. Oxygen reduction and nitrogen doping were achieved simultaneously under the hydrothermal reaction. Up to 5% nitrogen-doped graphene sheets with slightly wrinkled and folded feature were obtained at the relative low hydrothermal temperature. With the increase of hydrothermal temperature, the nitrogen content decreased slightly and more pyridinic N incorporated into the graphene network. Meanwhile, a jellyfish-like graphene structure was formed by self-organization of graphene sheets at the hydrothermal temperature of 160 °C. Further increase of the temperature to 200 °C, graphene sheets could self-aggregate into agglomerate particles but still contained doping level of 4 wt % N. The unique hydrothermal environment should play an important role in the nitrogen doping and the jellyfish-like graphene formation. This simple hydrothermal method could provide the synthesis of nitrogen-doped graphene sheets in large scale for various practical applications.

Rational introduction of electrocatalytically-active nanocrystals into carbon–sulfur enables the accelerated kinetics of sulfur redox reactions, thus achieving an ultra-high-rate and long-life Li–S battery.

Nitrogen-enriched mesoporous carbons with tunable nitrogen content and similar mesoporous structures have been prepared by a facile colloid silica nanocasting to house sulfur for lithium-sulfur batteries. The results give unequivocal proof that nitrogen doping could assist mesoporous carbon to suppress the shuttling phenomenon, possibly via an enhanced surface interaction between the basic nitrogen functionalities and polysulfide species. However, nitrogen doping only within an appropriate level can improve the electronic conductivity of the carbon matrix. Thus, the dependence of total electrochemical performance on the nitrogen content is nonmonotone. At an optimal nitrogen content of 8.1 wt %, the carbon/sulfur composites deliver a highest reversible discharge capacity of 758 mA h g(-1) at a 0.2 C rate and 620 mA h g(-1) at a 1 C rate after 100 cycles. Furthermore, with the assistance of PPy/PEG hybrid coating, the composites could further increase the reversible capacity to 891 mA h g(-1) after 100 cycles. These encouraging results suggest nitrogen doping and surface coating of the carbon hosts are good strategies to improve the performance carbon/sulfur-based cathodes for lithium-sulfur batteries.