Transition metal (M = Fe, Co, Ni) and Se codoped two-dimensional uniform NbS2 (MxNb1-xS2-ySey) nanosheets were synthesized via a facile oil-phase synthetic process. The morphology of MxNb1-xS2-ySey can be adjusted by tuning the amount of metal and Se introduced into NbS2. Among them, the optimized Fe0.3Nb0.7S1.6Se0.4 nanosheets, with lateral sizes of 1-2 μm and approximately 5 nm thick, achieve the best Li-ion and Na-ion storage properties. For example, the Fe0.3Nb0.7S1.6Se0.4 nanosheets depict excellent rate capabilities with fifth-cycle specific capacities of 461.3 mAh g-1 at 10 A g-1 for Li storage and 136 mAh g-1 at 5 A g-1 for Na storage. More significantly, ultralong cyclic stabilities were achieved with reversible specific capacities of 444 mAh g-1 at 5 A g-1 during the 3000th cycle for Li storage and 250 mAh g-1 at 1 A g-1 during the 750th cycle for Na storage. Post-treatment high-resolution transmission electron microscopy was studied to prove that the reversible Li-ion storage in NbS2 was based on a conversion reaction mechanism.
Keywords: Li storage; Na storage; NbS2 nanosheets; conversion reaction mechanism; oil phase.