A binary metal organic framework derived hierarchical hollow Ni₃S₂/Co₉S₈/N-doped carbon composite with superior sodium storage performance

A binary Ni/Co metal organic framework (Ni-Co-MOF) with a hollow-sphere structure that is decorated with cone-shaped protrusions was prepared via a facile solvothermal reaction. Carbonization and sulfurization of the Ni-Co-MOF produced a Ni₃S₂/Co₉S₈/N-doped carbon composite that retained the hierarchical structure. The final composite material presents exceptional electrochemical performance when used as an anode in sodium-ion batteries. A reversible specific capacity of 419.9 mA h g^-1 at a current density of 0.1 A g^-1 was achieved after 100 cycles, with an exceptional capacity retention of 98.6%. Furthermore, superior rate capability was also demonstrated: an average capacity of 323.2 mA h g^-1 at a current density of 2 A g^-1 can be achieved. This exceptional performance can be attributed to the unique nano-architecture derived from the MOF precursor, as the resultant material possesses an ideal profile for an excellent anode material: ultrafine Ni₃S₂ and Co₉S₈ particles (∼7 nm), a hollow, porous structure, and an ultrathin N-doped carbon coating.