Nitrogen-doped CMK-3@graphene hybrids as a sulfur host material for use in lithium-sulfur batteries

Sulfur as a cathode material has the advantages of low cost, high theoretical energy density and safety. However, the capacity decay and a shuttle effect are major problems that cause poor coulombic efficiency and a short cycling life. An ordered mesoporous carbon, CMK-3 was oxidized by 67% HNO₃, added to a graphene oxide suspension, sonicated, freeze-dried and annealed in NH₃ to obtain a nitrogen-doped CMK-3@graphene hybrid, which was melt-infiltrated with sulfur to prepare a cathode material for lithium-sulfur batteries. Results indicate that the CMK-3 particles are uniformly dispersed in graphene sheets and their surfaces are coated with graphene. The N-(CMK-3@G)/S has a reversible discharge capacity of 867.3 mAh·g^-1 after 300 cycles at a current density of 335 mA·g^-1 with a capacity retention of 82%. Compared with N-CMK-3/S and N-G/S cathodes, the rate performance and polarization characteristics are also improved. The graphene coating on CMK-3 traps soluble polysulfides during the charge/discharge process and nitrogen doping facilitates chemical adsorption of polysulfides to inhibit the shuttle effect, which together improve the performance of the battery.