NbS2 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 2 (M x Nb 1– x S 2– y Se y ) nanosheets were synthesized via a facile oil-phase synthetic process. The morphology of M x Nb 1– x S 2– y Se y can be adjusted by tuning the amount of metal and Se introduced into NbS 2 . Among them, the optimized Fe 0.3 Nb 0.7 S 1.6 Se 0.4 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 Fe 0.3 Nb 0.7 S 1.6 Se 0.4 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 NbS 2 was based on a conversion reaction mechanism.