Ligands induced NiS2 quantum dots for synchronous high specific capacity and robust stability of advanced electrochemical energy storage

The structural collapse of transition metal sulfides in repeated charge and discharge process restricts their cyclic performance. How to effectively remedy stability without sacrifice of capacity still remains a daunting challenge. Herein, ultra-small NiS2 quantum dots (QDs) are assembled with pyridine ligands containing heterocyclic nitrogen atoms of high electronegativity. The induction of electron cloud of heterocyclic nitrogen shortens the NiS bond with stronger structural stability. Besides, the localized lone pair of electrons near nickel atoms reduces the repulsive force to the diffused OH− ions, thus increasing affinity of the redox reaction. Benefiting from the tailor-made of ligands and size effect of QDs, a great promotion in both specific capacity of 651.8 C∙g−1 at 1 A∙g−1 and stability of 94.7% retention at 5 A∙g−1 over 8000 cycles is achieved as compared to ordinary bulk materials. These results demonstrate that ligands induced QDs is a promising strategy for precisely regulating metal sulfide electrode materials of advanced energy storage devices.