A g-C3N4 self-templated preparation of N-doped carbon nanosheets@Co-Co3O4/Carbon nanotubes as high-rate lithium-ion batteries' anode materials.

Abstract A novel N-doped graphene-like carbon nanosheets (CNs) and carbon nanotubes (CNTs)-encapsulated Co-Co3O4 nanoparticles (NPs) (CN@Co-Co3O4/CNTs) were synthesized successfully by a simple hydrothermal and annealing method with graphite carbon nitride (g-C3N4) as self-template. By annealing Co2+/g-C3N4 under N2 atmosphere, g-C3N4 was transformed into CN/CNTs, and Co2+ was reduced into CoNPs which were embedded in CNs. Further annealing in air, a shell of Co3O4 was formed around CoNPs. The amount of CNs, CNTs, and CoNPs can be adjusted by changing the ratio of Co2+ in Co2+/g-C3N4. The graphene-like CNs provided a large number of active sites and a large specific surface area for loading lots of small CoNPs uniformly. The CNTs with a diameter of 100 nm could not only improve the conductivity but also provide a buffer space for the aggregation and volume expansion of Co3O4. CNTs also enlarged the interlayer distance of CNs, which prevented the re-stacking of CNs and provided great convince for the intercalation and de-intercalation of Li+. When applied for anode material of lithium-ion batteries, CN@Co-Co3O4/CNTs exhibited a high discharge capacity of 460.0 mAh g−1 at 5000 mA g−1 after 300 cycles with a Coulombic efficiency of 98% and excellent higher-rate capacity (401.0 mAh g−1 at 2000 mA g−1 and 329.0 mAh g−1 at 5000 mA g−1).