NbS Nanosheets with M/Se (M = Fe, Co, Ni) Codopants for Li and Na Storage.

Transition metal (M = Fe, Co, Ni) and Se codoped two-dimensional uniform NbS (MNbSSe) nanosheets were synthesized via a facile oil-phase synthetic process. The morphology of MNbSSe can be adjusted by tuning the amount of metal and Se introduced into NbS. Among them, the optimized FeNbSSe 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 FeNbSSe nanosheets depict excellent rate capabilities with fifth-cycle specific capacities of 461.3 mAh g at 10 A g for Li storage and 136 mAh g at 5 A g for Na storage. More significantly, ultralong cyclic stabilities were achieved with reversible specific capacities of 444 mAh g at 5 A g during the 3000th cycle for Li storage and 250 mAh g at 1 A g 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 NbS was based on a conversion reaction mechanism.