Using density functional theory (DFT) computations, we investigated pyridinelike structures in a series of single-walled $\mathrm{C}{\mathrm{N}}_x$ nanotubes and found that tube chirality and diameter play important roles in the formation of pyridinelike structures. Not pyridinelike structures but more ${\mathrm{N}}_{\mathrm{C}}$ defects (N atoms substituting for C atoms) should be responsible for the experimentally observed donor states of $\mathrm{C}{\mathrm{N}}_x$ nanotubes. The adsorption energies of Li at the pyridinelike defect are so large and the energy barrier for lithium penetrating the defect is so low that $\mathrm{C}{\mathrm{N}}_x$ nanotubes with pyridinelike structures have enhanced capability for lithium storage.

MoS₂/graphene composites were synthesized through the concurrent reducing of (NH₄)₂MoS₄ and graphene oxide sheets with assistance of different cationic surfactants (DTAB, OTAB and TBAB) followed by heat treatment in a nitrogen atmosphere. The effects of the three cationic surfactants on the microstructures and electrochemical performances of the composites for reversible lithium storage were investigated. The MoS₂ in the composites prepared with assistance of DTAB or OTAB displays single-/few-layer structure, while the layered MoS₂ sheets with about 6–7 layers are observed in the composite prepared with assistance of TBAB. The former two composites exhibit greatly enhanced electrochemical performance for reversible Li⁺ storage. In particular, MoS₂/graphene composite prepared with assistance of OTAB delivered a high reversible capacity of 1056 mA h g⁻¹ with excellent cycle stability and good rate capability. The significant improvement in the electrochemical performances is attributed to the roubest composite structure and the synergistic interactions between graphene and single-/few-layer MoS₂. This work also presented a facile process to prepare MoS₂/graphene composites, in which the layer number of MoS₂ sheets could be adjusted to a certain extent by using different cationic surfactants.