Design of pomegranate-like clusters with NiS₂ nanoparticles anchored on nitrogen-doped porous carbon for improved sodium ion storage performance

Nickel sulfide, a promising anode for sodium-ion batteries (SIBs), has drawn a lot of attention due to its natural abundance, low cost, rich types and high theoretical specific capacity (Ni₃S₂: 446, NiS: 591 and NiS₂: 879 mA h g^-1). However, the huge volume change induced severe electrode pulverization results in the low specific capacity and poor cycling stability of nickel sulfide electrodes. Herein, in this paper, we developed a metal-organic framework (MOF) strategy to prepare pomegranate-like clusters with small NiS₂ nanoparticles anchored on nitrogen doped porous graphitic carbon networks (NiS₂/NC) via successive carbonization and sulfidation. When evaluated as an anode for SIBs, the as-prepared NiS₂/NC hybrid exhibited a high reversible capacity of 505.7 mA h g^-1 after 100 cycles at 0.1 A g^-1, excellent rate capability (294.4 mA h g^-1 at 3 A g^-1) and robust cycling stability with a capacity of 356.2 mA h g^-1 after 300 cycles at 0.5 A g^-1, which outperforms most of the nickel sulfide based electrodes reported so far. The excellent cycling performance and rate capability for SIBs can be attributed to the unique structure inherited from nickel based MOFs, in situ fabrication strategy, high capacity of NiS₂, and conductive and buffering features of the nitrogen-doped graphitic carbon networks, demonstrating the great potential of the as-prepared NiS₂/NC hybrid for high-performance SIBs.